You can change the requested URL in the HTTPCaller to this URL:

https://postman-echo.com/get

or POST etc.

This will give back what FME send as JSON file. And you can analyse this to see if FME did something unexpected.

Hi exc,

This is indeed a problem with the http caller transformer. Are you able to share the call you are trying to make or is it sensitive information? What i usually do is try to send the most barebones call to the API that should work and check the response. Usually I hope to get a not authorized page, if I don't then I try to tweak the url and the headers. Then I add my authorization, and then I add the body that contains information that the API call needs to function.

What I do this way is 1: check if my url is correct, 2: check if the authorization is correct and 3: check if the body layout is correct. This way you can sort of find where you have a problem. 

I hope this helps you a little bit with tracking down your problem.

I was typing out this follow up question to jkr_wrk:

Can you please elaborate on this?

** It will give back what FME sent as a JSON “file”? **
Where do I find that file? When doing this, I do not find any difference to what is in the Transaction Log.

However, I then noticed I got an Output result, rather than a <Rejected> result.  The Output _response_body field (default) has the header info in it.

This allowed me to determine that the FME web connection stores an obtained access token in the variable named eTOKEN].

This was very helpful in determining how to configure API Call Parameter-Header Format for a custom web service based on the Token template:

     Authorization: Bearer iTOKEN]