I've seen this happen a few times in different scenarios - I'm not sure what triggers this issue.
- When the profile is initially recorded: HTTP Header Content-Type is set to application/json; charset=UTF-8
- I am able to execute the test many times without having an issue. During these executions Content-Type remains set to application/json; charset=UTF-8
- At some point test executions start sending messages with Content-Type set to text/plain; charset=UTF-8
-- this causes 415 Unsupported Media type errors.
Content Type is not null and disabled in Profile -> Properties -> HTTP Headers so to fix this issue I add another Content-Type header set to application/json; charset=UTF-8, checking the Overwrite box for each message with the issue.
I recently saw this issue occur in the following scenario but I think it has occurred in other scenarios as well: