Authentication problem using Postman with the trial version

I'm not aware of any issues specifically with the REST API within the trial scenario.

You say you're retrieving the token, I assume from /server/authenticationtoken?  Can you show the HTTP request you make there, with your user credentials obscured?

Here is the http request I used (per github instructions):

I notice you linked to the Postman library, but it doesn't look like you're using the sample authentication token request.  Is there a reason why not?

The issue is that the authentication tokens expects the credential and vault data as a JSON object in the body of the HTTP request, not in the URL as you have it there.  There's an example on the Developer Portal which you may also find useful: Authenticating to the M-Files Web Service (REST API)

Yes that was it!  I placed the credential and vault data in the params instead of the body!

Many thanks!

Tom