- This is Microsoft.
- He returns Webhook success with a code 200 and plaintext 1.
- He returns Webhook failure with a code 200 and a string tells its endpoint returned error 400.
- the string didn't tell what exactly the error.
- Don’t be like Microsoft.
EDIT: Got a few details wrong since this happens a few months ago and this meme used to be on r/ProgrammerHumor. Also the proof: 
It's hard when you hit an endpoint that hits another endpoint, because technically the first request IS a 200. No right or wrong way as long as they are consistent and document it clearly imo
Now here is the fun part: they do not have a API documentation; they only have a very generic guide on how to setup webhook API
Microsoft code docs are the literal worst
Microsoft docs in general are the worst. Can't tell you how many fucking dead links and straight up incorrect information I've come across on their official help articles
Or deprecated documentation that has no indicator whatsoever that it's out of date