I've encountered this today and on my end, the issue was fixed by selecting "V1" even if it says "deprecated" at Postman's export page. It seems Postman's v2.1 cannot be processed properly into SoapUI as well. For more details on the steps for fix, you can refer to this page: https://www.soapui.org/docs/postman-collections.html
"an Engineer without a degree, a QA tester without any official certification (just yet 😉 ) "
I have imported your file which you have enclosed with the problem. Seems like, there is no problem with the JSON file. It works fine. Below is the screenshot after I imported the JSON. Try using latest version of postman.
Thanks for replying. sorry I didn't mention it clearly. I mean I was trying to import the postman collection file in the SoapUI or ReadyAPI via File/Import Postman collection. Both of them give the error.