Why do we need source xml files for SOAP API security testing?

Question

API

Good day!
Hope everyone is in good health at this not exactly easy time.

I have come across the following situation. The guys from my team were doing SOAP API penetration testing for one of our clients. Now it's time for a retest, and the colleague who did the original test is now on vacation. After talking to him, he told me that I need to ask the customer for XML (WSDL etc) files to fully test that API, since otherwise it will not be possible to generate requests to the API or the responses will be incorrect.
For the first time I hear that we need initial XML files for the API for testing. Isn't the API URL itself sufficient when using tools like SOAP UI (example: https://api.my.com/test/proxyservice/getdata?wsdl) ?