APM-000 AMP-941 API Specs - add Errors section

Author: SachinPath

specification/mesh-api.yaml

@@ -267,8 +267,16 @@ info:
     For more details, and to get started, see [digital onboarding](https://digital.nhs.uk/developer/guides-and-documentation/digital-onboarding#using-the-digital-onboarding-portal). 
     
     For any other queries, contact our support mailbox [ssd.nationalservicedesk@nhs.net](mailto:ssd.nationalservicedesk@nhs.net).
-    
 
+    ## Errors
+    We use standard HTTP status codes to show whether an API request succeeded or not. They are usually in the range:
+
+    * 200 to 299 if it succeeded, including code 202 if it was accepted by an API that needs to wait for further action
+    * 400 to 499 if it failed because of a client error by your application
+    * 500 to 599 if it failed because of an error on our server
+    
+    Errors specific to each API are shown in the Endpoints section, under Response. See our [reference guide](https://digital.nhs.uk/developer/guides-and-documentation/reference-guide#http-status-codes) for more on errors.
+    
   title: Message Exchange for Social Care and Health - REST API
   version: v1.0.168-alpha
 openapi: 3.0.2