diff --git a/Model/Api.php b/Model/Api.php
index bc42d1b..a5ee765 100644
--- a/Model/Api.php
+++ b/Model/Api.php
@@ -384,13 +384,15 @@ public function lookupTaxes($itemsByType, $shippingAssignment, $quote)
         }
 
         if (isset($itemsByType[self::ITEM_TYPE_SHIPPING])) {
+            $addressShippingAmount = (float) $address->getShippingAmount();
             foreach ($itemsByType[self::ITEM_TYPE_SHIPPING] as $code => $itemTaxDetail) {
                 // Shipping as a cart item - shipping needs to be taxed
+                $shippingRowTotal = $itemTaxDetail[self::KEY_ITEM]->getRowTotal();
                 $cartItems[] = array(
                     'ItemID' => 'shipping',
                     'Index' => $index++,
                     'TIC' => $this->productTicService->getShippingTic(),
-                    'Price' => $itemTaxDetail[self::KEY_ITEM]->getRowTotal(),
+                    'Price' => ($shippingRowTotal ?: $addressShippingAmount),
                     'Qty' => 1,
                 );
             }
@@ -429,7 +431,22 @@ public function lookupTaxes($itemsByType, $shippingAssignment, $quote)
             ),
         );
 
-        // hash, check cache
+        // Call before event (observers may modify $params, e.g. address verification)
+        $lookupParamsHolder = $this->objectFactory->create();
+        $lookupParamsHolder->setParams($params);
+
+        $this->eventManager->dispatch('taxcloud_lookup_before', array(
+            'obj' => $lookupParamsHolder,
+            'customer' => $customer,
+            'address' => $address,
+            'quote' => $quote,
+            'itemsByType' => $itemsByType,
+            'shippingAssignment' => $shippingAssignment,
+        ));
+
+        $params = $lookupParamsHolder->getParams();
+
+        // hash, check cache (use post-observer params so cache key matches what we send to TaxCloud)
         $cacheKeyApi = 'taxcloud_rates_' . hash('sha256', json_encode($params));
         $cacheResult = null;
         if ($this->cacheType->load($cacheKeyApi)) {
@@ -448,21 +465,6 @@ public function lookupTaxes($itemsByType, $shippingAssignment, $quote)
             return $result;
         }
 
-        // Call before event
-        $obj = $this->objectFactory->create();
-        $obj->setParams($params);
-
-        $this->eventManager->dispatch('taxcloud_lookup_before', array(
-            'obj' => $obj,
-            'customer' => $customer,
-            'address' => $address,
-            'quote' => $quote,
-            'itemsByType' => $itemsByType,
-            'shippingAssignment' => $shippingAssignment,
-        ));
-
-        $params = $obj->getParams();
-
         // Call the TaxCloud web service
 
         $this->tclogger->info('Calling lookupTaxes LIVE API');
diff --git a/Observer/Sales/Address.php b/Observer/Sales/Address.php
index ec18bb2..5b36c1e 100644
--- a/Observer/Sales/Address.php
+++ b/Observer/Sales/Address.php
@@ -96,6 +96,8 @@ public function execute(
         $result = $this->tcapi->verifyAddress($params['destination']);
 
         if ($result) {
+            $result['Address1'] = $result['Address1'] ?: ($params['destination']['Address1'] ?? '');
+            $result['Address2'] = $result['Address2'] ?: ($params['destination']['Address2'] ?? '');
             $params['destination'] = $result;
             $obj->setParams($params);
         }
diff --git a/Test/Unit/Mocks/MagentoMocks.php b/Test/Unit/Mocks/MagentoMocks.php
index 9ec7806..672381a 100644
--- a/Test/Unit/Mocks/MagentoMocks.php
+++ b/Test/Unit/Mocks/MagentoMocks.php
@@ -202,6 +202,7 @@ class Event
     {
         public function getName() { return ''; }
         public function getOrder() { return null; }
+        public function getObj() { return null; }
     }
 }
 
@@ -335,6 +336,8 @@ public function debug($message) { /* do nothing */ }
 namespace Magento\Quote\Model {
     class Quote
     {
+        public function getId() { return null; }
+        public function getCustomer() { return null; }
         public function getCustomerTaxClassId() { return null; }
         public function getStoreId() { return 1; }
     }
@@ -446,11 +449,16 @@ public function create();
 }
 
 namespace Magento\Customer\Api\Data {
+    interface CustomerInterface
+    {
+        public function getId();
+    }
+
     interface AddressInterfaceFactory
     {
         public function create();
     }
-    
+
     interface RegionInterfaceFactory
     {
         public function create();
diff --git a/Test/Unit/Model/ApiTest.php b/Test/Unit/Model/ApiTest.php
index 85ae9c6..e3c3525 100644
--- a/Test/Unit/Model/ApiTest.php
+++ b/Test/Unit/Model/ApiTest.php
@@ -628,4 +628,212 @@ public function testGetOrderDetailsReturnsNullWhenNotOkOrError()
 
         $this->assertNull($result, 'getOrderDetails should return null when ResponseType is not OK');
     }
+
+    /**
+     * lookupTaxes: when shipping row total is 0, uses address getShippingAmount() for shipping price sent to TaxCloud.
+     */
+    public function testLookupTaxesUsesAddressShippingAmountWhenShippingRowTotalIsZero()
+    {
+        $this->scopeConfig->method('getValue')
+            ->willReturnMap([
+                ['tax/taxcloud_settings/enabled', \Magento\Store\Model\ScopeInterface::SCOPE_STORE, null, '1'],
+                ['tax/taxcloud_settings/logging', \Magento\Store\Model\ScopeInterface::SCOPE_STORE, null, '0'],
+                ['tax/taxcloud_settings/api_id', \Magento\Store\Model\ScopeInterface::SCOPE_STORE, null, 'test_api_id'],
+                ['tax/taxcloud_settings/api_key', \Magento\Store\Model\ScopeInterface::SCOPE_STORE, null, 'test_api_key'],
+                ['tax/taxcloud_settings/cache_lifetime', \Magento\Store\Model\ScopeInterface::SCOPE_STORE, null, '0'],
+                ['tax/taxcloud_settings/guest_customer_id', \Magento\Store\Model\ScopeInterface::SCOPE_STORE, null, '-1'],
+                ['shipping/origin/postcode', \Magento\Store\Model\ScopeInterface::SCOPE_STORE, null, '60005'],
+                ['shipping/origin/street_line1', \Magento\Store\Model\ScopeInterface::SCOPE_STORE, null, '71 W Seegers Rd'],
+                ['shipping/origin/street_line2', \Magento\Store\Model\ScopeInterface::SCOPE_STORE, null, ''],
+                ['shipping/origin/city', \Magento\Store\Model\ScopeInterface::SCOPE_STORE, null, 'Arlington Heights'],
+                ['shipping/origin/region_id', \Magento\Store\Model\ScopeInterface::SCOPE_STORE, null, '1'],
+            ]);
+
+        $region = $this->createMock(\Magento\Directory\Model\Region::class);
+        $region->method('load')->willReturnSelf();
+        $region->method('getCode')->willReturn('GA');
+        $this->regionFactory->method('create')->willReturn($region);
+
+        $customer = $this->createMock(\Magento\Customer\Api\Data\CustomerInterface::class);
+        $customer->method('getId')->willReturn(1);
+
+        $quote = $this->createMock(\Magento\Quote\Model\Quote::class);
+        $quote->method('getCustomer')->willReturn($customer);
+
+        $address = $this->createMock(\Magento\Quote\Model\Quote\Address::class);
+        $address->method('getPostcode')->willReturn('30097');
+        $address->method('getStreet')->willReturn(['405 Victorian Ln']);
+        $address->method('getCity')->willReturn('Duluth');
+        $address->method('getRegionId')->willReturn(1);
+        $address->method('getCountryId')->willReturn('US');
+        $address->method('getShippingAmount')->willReturn(13.85);
+
+        $shipping = $this->createMock(\Magento\Quote\Model\Quote\Address::class);
+        $shipping->method('getAddress')->willReturn($address);
+
+        $shippingAssignment = $this->createMock(\Magento\Quote\Api\Data\ShippingAssignmentInterface::class);
+        $shippingAssignment->method('getShipping')->willReturn($shipping);
+        $shippingAssignment->method('getItems')->willReturn([]);
+
+        $shippingTaxDetailItem = $this->createMock(\Magento\Tax\Api\Data\QuoteDetailsItemInterface::class);
+        $shippingTaxDetailItem->method('getRowTotal')->willReturn(0);
+
+        $itemsByType = [
+            Api::ITEM_TYPE_SHIPPING => [
+                'shipping' => [Api::KEY_ITEM => $shippingTaxDetailItem],
+            ],
+        ];
+
+        $this->productTicService->method('getShippingTic')->willReturn('11010');
+
+        $this->cacheType->method('load')->willReturn(false);
+
+        $capturedParams = null;
+        $this->mockDataObject->method('setParams')->willReturnCallback(function ($p) use (&$capturedParams) {
+            $capturedParams = $p;
+            return $this->mockDataObject;
+        });
+        $this->mockDataObject->method('getParams')->willReturnCallback(function () use (&$capturedParams) {
+            return $capturedParams;
+        });
+        $this->mockDataObject->method('setResult')->willReturnSelf();
+        $this->mockDataObject->method('getResult')->willReturn([
+            'ResponseType' => 'OK',
+            'CartItemsResponse' => ['CartItemResponse' => [['CartItemIndex' => 0, 'TaxAmount' => 0]]],
+        ]);
+        $this->objectFactory->method('create')->willReturn($this->mockDataObject);
+
+        $lookupParams = null;
+        $mockLookupResponse = new \stdClass();
+        $mockLookupResponse->LookupResult = new \stdClass();
+        $mockLookupResponse->LookupResult->ResponseType = 'OK';
+        $mockLookupResponse->LookupResult->CartItemsResponse = new \stdClass();
+        $mockLookupResponse->LookupResult->CartItemsResponse->CartItemResponse = [
+            (object)['CartItemIndex' => 0, 'TaxAmount' => 0],
+        ];
+        $this->mockSoapClient->method('lookup')->willReturnCallback(function ($params) use (&$lookupParams, $mockLookupResponse) {
+            $lookupParams = $params;
+            return $mockLookupResponse;
+        });
+
+        $this->api->lookupTaxes($itemsByType, $shippingAssignment, $quote);
+
+        $this->assertNotNull($lookupParams, 'lookup should have been called');
+        $cartItems = $lookupParams['cartItems'] ?? [];
+        $shippingItem = null;
+        foreach ($cartItems as $item) {
+            if (isset($item['ItemID']) && $item['ItemID'] === 'shipping') {
+                $shippingItem = $item;
+                break;
+            }
+        }
+        $this->assertNotNull($shippingItem, 'cartItems should contain shipping');
+        $this->assertSame(13.85, (float) $shippingItem['Price'], 'lookupTaxes should send address getShippingAmount() when shipping row total is 0');
+    }
+
+    /**
+     * lookupTaxes: cache key is computed from params after taxcloud_lookup_before event.
+     */
+    public function testLookupTaxesCacheKeyUsesParamsAfterEvent()
+    {
+        $this->scopeConfig->method('getValue')
+            ->willReturnMap([
+                ['tax/taxcloud_settings/enabled', \Magento\Store\Model\ScopeInterface::SCOPE_STORE, null, '1'],
+                ['tax/taxcloud_settings/logging', \Magento\Store\Model\ScopeInterface::SCOPE_STORE, null, '0'],
+                ['tax/taxcloud_settings/api_id', \Magento\Store\Model\ScopeInterface::SCOPE_STORE, null, 'test_api_id'],
+                ['tax/taxcloud_settings/api_key', \Magento\Store\Model\ScopeInterface::SCOPE_STORE, null, 'test_api_key'],
+                ['tax/taxcloud_settings/cache_lifetime', \Magento\Store\Model\ScopeInterface::SCOPE_STORE, null, '3600'],
+                ['tax/taxcloud_settings/guest_customer_id', \Magento\Store\Model\ScopeInterface::SCOPE_STORE, null, '-1'],
+                ['shipping/origin/postcode', \Magento\Store\Model\ScopeInterface::SCOPE_STORE, null, '60005'],
+                ['shipping/origin/street_line1', \Magento\Store\Model\ScopeInterface::SCOPE_STORE, null, '71 W Seegers Rd'],
+                ['shipping/origin/street_line2', \Magento\Store\Model\ScopeInterface::SCOPE_STORE, null, ''],
+                ['shipping/origin/city', \Magento\Store\Model\ScopeInterface::SCOPE_STORE, null, 'Arlington Heights'],
+                ['shipping/origin/region_id', \Magento\Store\Model\ScopeInterface::SCOPE_STORE, null, '1'],
+            ]);
+
+        $region = $this->createMock(\Magento\Directory\Model\Region::class);
+        $region->method('load')->willReturnSelf();
+        $region->method('getCode')->willReturn('GA');
+        $this->regionFactory->method('create')->willReturn($region);
+
+        $customer = $this->createMock(\Magento\Customer\Api\Data\CustomerInterface::class);
+        $customer->method('getId')->willReturn(1);
+        $quote = $this->createMock(\Magento\Quote\Model\Quote::class);
+        $quote->method('getCustomer')->willReturn($customer);
+
+        $address = $this->createMock(\Magento\Quote\Model\Quote\Address::class);
+        $address->method('getPostcode')->willReturn('30097');
+        $address->method('getStreet')->willReturn(['405 Victorian Ln']);
+        $address->method('getCity')->willReturn('Duluth');
+        $address->method('getRegionId')->willReturn(1);
+        $address->method('getCountryId')->willReturn('US');
+        $address->method('getShippingAmount')->willReturn(0);
+
+        $shipping = $this->createMock(\Magento\Quote\Model\Quote\Address::class);
+        $shipping->method('getAddress')->willReturn($address);
+        $shippingAssignment = $this->createMock(\Magento\Quote\Api\Data\ShippingAssignmentInterface::class);
+        $shippingAssignment->method('getShipping')->willReturn($shipping);
+        $shippingAssignment->method('getItems')->willReturn([]);
+
+        $shippingTaxDetailItem = $this->createMock(\Magento\Tax\Api\Data\QuoteDetailsItemInterface::class);
+        $shippingTaxDetailItem->method('getRowTotal')->willReturn(0);
+        $itemsByType = [
+            Api::ITEM_TYPE_SHIPPING => [
+                'shipping' => [Api::KEY_ITEM => $shippingTaxDetailItem],
+            ],
+        ];
+
+        $this->productTicService->method('getShippingTic')->willReturn('11010');
+        $this->cacheType->method('load')->willReturn(false);
+
+        $modifiedDestination = [
+            'Address1' => 'Modified Street By Observer',
+            'Address2' => '',
+            'City' => 'Duluth',
+            'State' => 'GA',
+            'Zip5' => '30097',
+            'Zip4' => '',
+        ];
+        $this->mockDataObject->method('setParams')->willReturnSelf();
+        $this->mockDataObject->method('getParams')->willReturnCallback(function () use ($modifiedDestination) {
+            $base = [
+                'apiLoginID' => 'test_api_id',
+                'apiKey' => 'test_api_key',
+                'customerID' => 1,
+                'cartID' => null,
+                'cartItems' => [['ItemID' => 'shipping', 'Index' => 0, 'TIC' => '11010', 'Price' => 0, 'Qty' => 1]],
+                'origin' => ['Address1' => '71 W Seegers Rd', 'City' => 'Arlington Heights', 'State' => 'GA', 'Zip5' => '60005', 'Zip4' => null],
+                'destination' => $modifiedDestination,
+                'deliveredBySeller' => false,
+                'exemptCert' => ['CertificateID' => null],
+            ];
+            return $base;
+        });
+        $this->mockDataObject->method('setResult')->willReturnSelf();
+        $this->mockDataObject->method('getResult')->willReturn([
+            'ResponseType' => 'OK',
+            'CartItemsResponse' => ['CartItemResponse' => [['CartItemIndex' => 0, 'TaxAmount' => 0]]],
+        ]);
+        $this->objectFactory->method('create')->willReturn($this->mockDataObject);
+
+        $cacheKeyUsed = null;
+        $this->cacheType->method('load')->willReturnCallback(function ($key) use (&$cacheKeyUsed) {
+            $cacheKeyUsed = $key;
+            return false;
+        });
+
+        $mockLookupResponse = new \stdClass();
+        $mockLookupResponse->LookupResult = new \stdClass();
+        $mockLookupResponse->LookupResult->ResponseType = 'OK';
+        $mockLookupResponse->LookupResult->CartItemsResponse = new \stdClass();
+        $mockLookupResponse->LookupResult->CartItemsResponse->CartItemResponse = [
+            (object)['CartItemIndex' => 0, 'TaxAmount' => 0],
+        ];
+        $this->mockSoapClient->method('lookup')->willReturn($mockLookupResponse);
+
+        $this->api->lookupTaxes($itemsByType, $shippingAssignment, $quote);
+
+        $expectedKey = 'taxcloud_rates_' . hash('sha256', json_encode($this->mockDataObject->getParams()));
+        $this->assertSame($expectedKey, $cacheKeyUsed, 'lookupTaxes cache key should be computed from params after taxcloud_lookup_before event');
+    }
 } 
\ No newline at end of file
diff --git a/Test/Unit/Observer/Sales/AddressTest.php b/Test/Unit/Observer/Sales/AddressTest.php
new file mode 100644
index 0000000..531ea51
--- /dev/null
+++ b/Test/Unit/Observer/Sales/AddressTest.php
@@ -0,0 +1,160 @@
+<?php
+/**
+ * Taxcloud_Magento2
+ *
+ * NOTICE OF LICENSE
+ *
+ * This source file is subject to the Open Software License (OSL 3.0)
+ */
+
+namespace Taxcloud\Magento2\Test\Unit\Observer\Sales;
+
+use PHPUnit\Framework\TestCase;
+use Taxcloud\Magento2\Observer\Sales\Address;
+
+class AddressTest extends TestCase
+{
+    /**
+     * When verify_address is disabled, observer returns early and does not call verifyAddress.
+     */
+    public function testExecuteDoesNothingWhenVerifyAddressDisabled()
+    {
+        $scopeConfig = $this->createMock(\Magento\Framework\App\Config\ScopeConfigInterface::class);
+        $scopeConfig->method('getValue')
+            ->willReturnMap([
+                ['tax/taxcloud_settings/enabled', \Magento\Store\Model\ScopeInterface::SCOPE_STORE, null, '1'],
+                ['tax/taxcloud_settings/verify_address', \Magento\Store\Model\ScopeInterface::SCOPE_STORE, null, '0']
+            ]);
+
+        $tcapi = $this->createMock(\Taxcloud\Magento2\Model\Api::class);
+        $tcapi->expects($this->never())->method('verifyAddress');
+
+        $logger = $this->createMock(\Taxcloud\Magento2\Logger\Logger::class);
+
+        $observer = new Address($scopeConfig, $tcapi, $logger);
+
+        $event = $this->createMock(\Magento\Framework\Event::class);
+        $observerObj = $this->createMock(\Magento\Framework\Event\Observer::class);
+        $observerObj->method('getEvent')->willReturn($event);
+
+        $observer->execute($observerObj);
+    }
+
+    /**
+     * When verifyAddress returns a result with empty Address1, observer preserves original Address1/Address2.
+     */
+    public function testExecutePreservesStreetWhenVerifiedResultHasEmptyAddress1()
+    {
+        $scopeConfig = $this->createMock(\Magento\Framework\App\Config\ScopeConfigInterface::class);
+        $scopeConfig->method('getValue')
+            ->willReturnMap([
+                ['tax/taxcloud_settings/enabled', \Magento\Store\Model\ScopeInterface::SCOPE_STORE, null, '1'],
+                ['tax/taxcloud_settings/verify_address', \Magento\Store\Model\ScopeInterface::SCOPE_STORE, null, '1']
+            ]);
+
+        $originalDestination = [
+            'Address1' => '405 Victorian Ln',
+            'Address2' => 'Apt 2',
+            'City' => 'Duluth',
+            'State' => 'GA',
+            'Zip5' => '30097',
+            'Zip4' => '',
+        ];
+
+        $verifiedResult = [
+            'Address1' => '',
+            'Address2' => '',
+            'City' => 'Duluth',
+            'State' => 'GA',
+            'Zip5' => '30097',
+            'Zip4' => '',
+        ];
+
+        $tcapi = $this->createMock(\Taxcloud\Magento2\Model\Api::class);
+        $tcapi->method('verifyAddress')->with($originalDestination)->willReturn($verifiedResult);
+
+        $logger = $this->createMock(\Taxcloud\Magento2\Logger\Logger::class);
+
+        $params = [
+            'destination' => $originalDestination,
+            'origin' => [],
+        ];
+
+        $obj = $this->getMockBuilder(\Magento\Framework\DataObject::class)
+            ->disableOriginalConstructor()
+            ->addMethods(['setParams', 'getParams'])
+            ->getMock();
+        $obj->method('getParams')->willReturn($params);
+        $obj->expects($this->once())->method('setParams')->with($this->callback(function ($updated) use ($originalDestination) {
+            return isset($updated['destination']['Address1'])
+                && $updated['destination']['Address1'] === $originalDestination['Address1']
+                && isset($updated['destination']['Address2'])
+                && $updated['destination']['Address2'] === $originalDestination['Address2'];
+        }))->willReturnSelf();
+
+        $event = $this->createMock(\Magento\Framework\Event::class);
+        $event->method('getObj')->willReturn($obj);
+
+        $observerObj = $this->createMock(\Magento\Framework\Event\Observer::class);
+        $observerObj->method('getEvent')->willReturn($event);
+
+        $observer = new Address($scopeConfig, $tcapi, $logger);
+        $observer->execute($observerObj);
+    }
+
+    /**
+     * When verifyAddress returns a result with non-empty Address1, observer uses verified result as-is.
+     */
+    public function testExecuteUsesVerifiedDestinationWhenAddress1IsPresent()
+    {
+        $scopeConfig = $this->createMock(\Magento\Framework\App\Config\ScopeConfigInterface::class);
+        $scopeConfig->method('getValue')
+            ->willReturnMap([
+                ['tax/taxcloud_settings/enabled', \Magento\Store\Model\ScopeInterface::SCOPE_STORE, null, '1'],
+                ['tax/taxcloud_settings/verify_address', \Magento\Store\Model\ScopeInterface::SCOPE_STORE, null, '1']
+            ]);
+
+        $originalDestination = [
+            'Address1' => '405 Victorian Ln',
+            'Address2' => '',
+            'City' => 'Duluth',
+            'State' => 'GA',
+            'Zip5' => '30097',
+            'Zip4' => '',
+        ];
+
+        $verifiedResult = [
+            'Address1' => '405 Victorian Ln',
+            'Address2' => 'Unit B',
+            'City' => 'Duluth',
+            'State' => 'GA',
+            'Zip5' => '30097',
+            'Zip4' => '1234',
+        ];
+
+        $tcapi = $this->createMock(\Taxcloud\Magento2\Model\Api::class);
+        $tcapi->method('verifyAddress')->with($originalDestination)->willReturn($verifiedResult);
+
+        $logger = $this->createMock(\Taxcloud\Magento2\Logger\Logger::class);
+
+        $params = ['destination' => $originalDestination];
+
+        $obj = $this->getMockBuilder(\Magento\Framework\DataObject::class)
+            ->disableOriginalConstructor()
+            ->addMethods(['setParams', 'getParams'])
+            ->getMock();
+        $obj->method('getParams')->willReturn($params);
+        $obj->expects($this->once())->method('setParams')->with($this->callback(function ($updated) use ($verifiedResult) {
+            return $updated['destination'] === $verifiedResult;
+        }))->willReturnSelf();
+
+        $event = $this->createMock(\Magento\Framework\Event::class);
+        $event->method('getObj')->willReturn($obj);
+
+        $observerObj = $this->createMock(\Magento\Framework\Event\Observer::class);
+        $observerObj->method('getEvent')->willReturn($event);
+
+        $observer = new Address($scopeConfig, $tcapi, $logger);
+        $observer->execute($observerObj);
+    }
+}