JSON parse error: response body is not valid JSON

The external endpoint returned an HTML error page (404, 500, authentication page) instead of JSON due to incorrect URL, authentication failure, or server error. (high likelihood)

The REST call timed out and received a partial response or proxy error page from network infrastructure or load balancers. (high likelihood)

The external API returned XML or plain text content when the REST message was configured to expect JSON response format. (medium likelihood)

Authentication credentials are invalid or expired, causing the external service to return an HTML login page or error page instead of API data. (medium likelihood)

The external endpoint URL has changed or the API version is deprecated, resulting in redirect pages or error messages in HTML format. (low likelihood)

Step 1: Navigate to System Web Services > Outbound > REST Message Logs to locate the failed REST call and examine the actual response body content.

Step 2: Check the HTTP status code in the REST message log - if it's 404, 401, 403, or 5xx, the endpoint URL or authentication needs correction before addressing JSON parsing.

Step 3: Verify the endpoint URL is correct by testing it directly in a browser or REST client tool like Postman to confirm it returns valid JSON.

Step 4: Review authentication settings in the REST message by checking HTTP headers, basic auth credentials, or OAuth configuration under the Authentication tab.

Step 5: Increase the timeout value in the REST message configuration if the response indicates timeout or partial content issues.

Step 6: Modify the REST message to handle non-JSON responses by checking the Content-Type header first or using try-catch logic in business rules before parsing JSON.

Step 7: Add error handling in your business rule or script to validate response format using responseBody.startsWith('{') before calling JSON.parse() or response.getBody().

Step 8: Test the corrected REST message using the Test functionality in the REST Message record to verify JSON parsing works before deploying to production.