What do we return from API Call

We have an endpoint that we call in automation with https post.
All it sends is a contactId and then the endpoint goes into the API, finds that contact,
and makes a change to a custom field.

The automation seems to get stuck on this step. It never goes to the next step.

Is there a log somewhere that I can look at that tells what is happening on the call?
Does the api endpoint need to return a 200 or some specific code that it succeeded?

I’m assuming you are referring to the “HTTP Post” node for automations here. There’s a help document available: https://help.keap.com/help/send-http-request

I would always ensure that your service always return a 200ish response (200 OK, 201 CREATED, 204 NO CONTENT, etc) to any request. If you aren’t returning a response at all then the request would be hanging until it timed out.