Invalid HTTP Method error is issued in the following situation:
Input parameters with Send In property set to 'Body' are not allowed for GET methods. Either change the (<method name>) method, or remove the input parameter
You are trying to change the place where the input parameter is sent, from URL to Body, and this is incompatible with the HTTP Method of the REST API Method, which is set to GET.
Either change the (
<method name>) method, or remove the input parameter.
Double-click on the error line to take you directly to the REST API method's property where the problem was detected.