I have this a lot where the request works fine in postman, but doesnt in readyapi! or soapui. You gotta remember postman doesnt include all the functionality that soapui and readyapi! include to allow the user to tailor their requests....thats why i think this occurs so much.
What i do in this situation is i use Fiddler to proxy the requests. Fiddler is a tool that extracts all the RAW content from any tool that uses it as a proxy and allows you to compare the difference between what soapui sends and what postman sends. This then allows you to make the appropriate changes in soapui to get it to work.
if this helped answer the post, could you please mark it as 'solved'? Also if you consider whether the title of your post is relevant? Perhaps if the post is solved, it might make sense to update the Subject header field of the post to something more descriptive? This will help people when searching for problems. Ta