The WSKey setup changed slightly between 1.0 and 2.0. Depending on when you requested your WorldCat Search API WSKey, your key might need to be updated.
If your key is not working, please contact OCLC Support to have your key updated. Include the name of your key and any error message you are receiving.
WorldCat Search API 1.0 transition resources: https://www.oclc.org/developer/support/worldcat-search-transition.en.html