Importing the Postman collections might fail because some Sitecore Experience Commerce Postman API collections are in v1 format, which is not supported by Postman app v8 and later.
To resolve the issue, convert the affected Postman collections to v2.1.0 as follows:
npm -vFor example,
npm install -g postman-collection-transformer
postman-collection-transformer convert -i <path to input Postman collection file> -o <path where the output Postman file will be downloaded> -j 1.0.0 -p 2.1.0 -PFor more details regarding postman-collection-transformer refer to Converting Postman collections from v1 to v2.