ASP.NET - Web Services - Web Service method name is not valid

 I got the error "Web Service method name is not valid" in one of my legacy ASP.NET WebService application while accessing from postman. In the browser I was able to access the asmx and the method structure. But in postman it was failing.

 While doing research I found multiple reasons for that. In my case the issue was it has "ByRef" parameters.

Listing out all the reasons and will update if I found anything new.

When accessing your web service through postman, make sure that

1. You don't have ByRef parameters

2. The method is public (Reference)

3. The method is not static (Reference)

4. The class name in the asmx file matches with the  class name in which this method (message) is present (Reference)

5. In the Webservice URL the combination of asmx and the Web service method name (message name)  is correct