Unused Input Parameter error is issued in the following situation:
(<parameter name>) is not used by (<method name>) REST API method. Either use it in the (<method name>) URL path, change the (<parameter name>) Send In property, or delete it
You have an input parameter in a REST API method's list, but it's not part of the URL.
Follow the instructions in the error message to solve it.
Double-click on the error line to take you directly to the REST API method's input parameter where the problem was detected.