how to host my web api as a subfolder in already existing site in IIS

I am trying to host my web API is IIS. It throws http error 403.14 forbidden error.

I have hosted my Web API as separate site. it is working fine. But if i add as a subfolder then

the problem occurs. ex: Sites: My API is fine Sites: Some other Application inside this i add My API as a sub folder. This is not working

  HTTP Error 403.14 - Forbidden
 The Web server is configured to not list the contents of this directory.