What is the problem ASP.Net Core Error CS1061

Severity Code Description Project File Line Suppression State
Error CS1061 ‘IServiceCollection’ does not contain a definition for
‘AddDefaultIdentity’ and no accessible extension method
‘AddDefaultIdentity’ accepting a first argument of type
‘IServiceCollection’ could be found (are you missing a using directive
or an assembly
reference?) WebHesab C:UsersDELLsourcereposWebHesabWebHesabStartup.cs 36 Active

Web API Azure .net c# request, visible to others, content of URL

My question is, can someone see your full URL web API, that you developed when a user makes a request with that URL get/post/delete/put ? Can they see in network traffic your Web APIs URL that are being called?
Example of URL: https://webapiserver.azure.com/something/something/Username/password
Can you actually see these content when the request is being made from a user, lets say i am developing an Android application, and inside that application, i make these kind of API request, and i worrying about the security, if an ‘attacker’ can see the content..