On each request Action, there is an Execution Log tab, this shows you what has happened and if all went OK.
The table gives a quick overview of the execution, Date & Time, Trigger (Manual, Event or Cron Job), Status of the response and time it took to execute the call in milliseconds.
The View button opens a detail view of the request. It is easy to see if an issue was provided to the request and to what the URL and Body resolved to.
The last part of the detail log is the Response tab. This is what the request got back from the call. It can contain error messages or valid responses.
Valid response from a comment issue.
Two examples of error responses. These errors also come with an HTTP status which is shown in the table.
Issue Tab - Integrations
There is also an Integrations tab shown on the issue when there exists at least one REST call related to the issue.
Clicking on the View button will display more details about the call and its response.