This is what they have replied for the issue :-
Thank you for reaching out.I tried it on my end and this seems a bug. I have logged it. Unfortunately, there isn't a workaround for this bug.The JIRA# is RIA-6725.
I have a comment on RIA-6725. According to the documentation - https://support.smartbear.com/readyapi/docs/testing/integrations/postman.html .
ReadyAPI currently supports only v1 collections and does not support v2 collections. So, RIA-6725 was converted to improvement request RIA-6640.
Export collection as V1 option. it works though deprecated.
I found a workaround by exporting the Postman Collection as Collection v1 (deprecated). However, authorization credentials are not imported in this way and you have to manually enter and save them in Soap UI requests.