How to respond to message shortcut in slack from postman?

I am working on a collection I want know when user trigger the message shortcut in slack it post the payload to the postman webhook URL(that I already created), after that my app should respond with an HTTP status 200 OK within 3000ms of receiving the payload.

I don’t know how to respond with HTTP status 200 OK, I know we can send data back to slack using response_url(that we received from the payload).

I know this can be possible using mock server but I can’t able to figure how to do that?

Can anyone help me with this issue?