If same session is maintained and if there are slow running transactions then ServiceNow returns 202 = Postman / integration has exceeded number of requests that can be processed using single thread.

If new / same session is used and if there are slow running transactions then ServiceNow returns 400 = ServiceNow is out of threads to accept new requests.

Post Trouble ticket API - 202

Video :

https://www.tutorialspoint.com/how-to-share-session-id-across-different-requests-in\-postman

https://www.servicenow.com/community/now-platform-blog/http-202\-from\-an-inbound-web-service-call/ba-p/2289402

https://support.servicenow.com/kb?id\=kb\_article\_view&sysparm\_article\=KB0961099