diff --git a/lib/open_invoice/entities/base.rb b/lib/open_invoice/entities/base.rb
index cd91b5c..e4650e5 100644
--- a/lib/open_invoice/entities/base.rb
+++ b/lib/open_invoice/entities/base.rb
@@ -9,6 +9,7 @@ class Base
 
       def initialize(supplier_uuid)
         @supplier_uuid = supplier_uuid
+        @api_version = "v1"
       end
 
       def self.request(*args)
diff --git a/lib/open_invoice/entities/buyer.rb b/lib/open_invoice/entities/buyer.rb
index b723dc6..34d932e 100644
--- a/lib/open_invoice/entities/buyer.rb
+++ b/lib/open_invoice/entities/buyer.rb
@@ -2,7 +2,7 @@ module OpenInvoice
   module Entities
     class Buyer < Base
       def index(opts = {})
-        request(:get, "/supplier/#{supplier_uuid}/buyers", opts)
+        request(:get, "/#{@api_version}/supplier/#{supplier_uuid}/buyers", opts)
       end
     end
   end
diff --git a/lib/open_invoice/entities/invoice.rb b/lib/open_invoice/entities/invoice.rb
index 7e98ef3..4c0ba1f 100644
--- a/lib/open_invoice/entities/invoice.rb
+++ b/lib/open_invoice/entities/invoice.rb
@@ -4,15 +4,15 @@ module OpenInvoice
   module Entities
     class Invoice < Base
       def index(opts = {})
-        request(:get, "/supplier/#{supplier_uuid}/invoices/page", opts)
+        request(:get, "/#{@api_version}/supplier/#{supplier_uuid}/invoices/page", opts)
       end
 
       def attachments(invoice_id, opts = {})
-        request(:get, "/supplier/#{supplier_uuid}/invoices/#{invoice_id}/attachments", opts)
+        request(:get, "/#{@api_version}/supplier/#{supplier_uuid}/invoices/#{invoice_id}/attachments", opts)
       end
 
       def download_attachment(invoice_id, attachment_id, file_path, opts)
-        attachment_url = "/supplier/#{@supplier_uuid}/invoices/#{invoice_id}/attachments/#{attachment_id}"
+        attachment_url = "/#{@api_version}/supplier/#{@supplier_uuid}/invoices/#{invoice_id}/attachments/#{attachment_id}"
         dirname = File.dirname(file_path)
         opts[:stream_body] = true
         FileUtils.mkdir_p(dirname) unless File.directory?(dirname)
@@ -39,7 +39,7 @@ def download_attachment(invoice_id, attachment_id, file_path, opts)
       end
 
       def history(invoice_id, opts = {})
-        request(:get, "/supplier/#{@supplier_uuid}/invoices/#{invoice_id}/history", opts)
+        request(:get, "/#{@api_version}/supplier/#{@supplier_uuid}/invoices/#{invoice_id}/history", opts)
       end
     end
   end
diff --git a/lib/open_invoice/entities/payment.rb b/lib/open_invoice/entities/payment.rb
index b3987ca..2ae13d3 100644
--- a/lib/open_invoice/entities/payment.rb
+++ b/lib/open_invoice/entities/payment.rb
@@ -2,7 +2,7 @@ module OpenInvoice
   module Entities
     class Payment < Base
       def index(opts = {})
-        request(:get, "/supplier/#{supplier_uuid}/payment", opts)
+        request(:get, "/#{@api_version}/supplier/#{supplier_uuid}/payment", opts)
       end
     end
   end
diff --git a/lib/open_invoice/entities/supplier.rb b/lib/open_invoice/entities/supplier.rb
index b3e2d94..a142025 100644
--- a/lib/open_invoice/entities/supplier.rb
+++ b/lib/open_invoice/entities/supplier.rb
@@ -2,7 +2,7 @@ module OpenInvoice
   module Entities
     class Supplier < Base
       def index(opts = {})
-        request(:get, "/supplier/#{supplier_uuid}", opts)
+        request(:get, "/#{@api_version}/supplier/#{supplier_uuid}", opts)
       end
     end
   end
diff --git a/lib/open_invoice/entities/user.rb b/lib/open_invoice/entities/user.rb
index c8ec9b2..3e2275e 100644
--- a/lib/open_invoice/entities/user.rb
+++ b/lib/open_invoice/entities/user.rb
@@ -8,7 +8,7 @@ def initialize(user_uuid)
       end
 
       def get
-        request(:get, "/users/#{user_uuid}")
+        request(:get, "/#{@api_version}/users/#{user_uuid}")
       end
     end
   end