Merge pull request #596 from NHSDigital/APM-003-AMP-941---Add-Errors-section-to-the-spec

API Specs - add Errors section

Author: nhsd-david-wass

specification/e-referrals-service-api.yaml

@@ -238,6 +238,14 @@ info:
     
     In step 14: following receipt, review and acceptance of your signed Connection Agreement, the e-RS FHIR API Partners team will contact you to facilitate production access for your application.
     
+    ## 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.
+    
 
   contact:
     url: 'https://digital.nhs.uk/developer/help-and-support'