EDITED -
From your latest reply, it looks like you are not using webMethods API Gateway, but just trying to invoke the IS Flow service directly via an HTTP/S call through Postman. If this is the case, share the masked/sanitized URL - you haven’t provided any info to go on.
Also, you previously mentioned a 500 but now it’s an Access Denied?
Share the actual and full error message too.
Not to discourage you from asking questions, we are all learners, but this is not a forum-level question.
I recommend that you do the free officlal courses -
1. API Management Basic (link)
2. API Management Essentials (link)
The answer to your question is here (link).
KM
#API-Management#API-Gateway#Developer-Portal#webMethods