diff --git a/spec/openapi.yaml b/spec/openapi.yaml
index 42bde33..79bad4d 100644
--- a/spec/openapi.yaml
+++ b/spec/openapi.yaml
@@ -1303,7 +1303,8 @@ paths:
         - ```destination_number``` The destination number the message should be
         delivered to. This should be specified in E.164
           international format. For information on E.164, please refer to http://en.wikipedia.org/wiki/E.164.
-          A destination number is required.
+          A destination number is required.  
+        ⚠️ IMDA TLS Compliance Notice: From 1 April 2026, all requests sending messages to Singapore (+65) numbers must use TLS 1.3 or higher. Requests using an older TLS version will be rejected with HTTP 422 Unprocessable Entity.
 
         - ```format``` The format specifies which format the message will be
         sent as, ```SMS``` (text message), ```MMS``` (multimedia message)