So after a few tests, I found out that this is just a generic message of anything that fails at slack at this point. I have first my endpoint that was unreachable. So it was returning this message. I fixed that, used ngrok for tunnel so that I could debug and that is how I found this issue.
Also, this error can occur due to the following reasons as well.
- Errors in code
- Unreachable backend or Invalidly configured slash command in the app