Unable to validate issuer when trying to access API

First: Given the standard, you manage just one Issuer.

Are you managing your own Identity / Token generation? It sounds like this isn't the case.

You could customize your API for creating your tokens explicitly. Then, you can indicate a global Issuer (like your project url) so anyone can validate against the same.

var token = new JwtSecurityToken(
                issuer: "http://my-perfect-proj.net",
                claims: ...,
                notBefore: DateTime.Now,
                expires: DateTime.Now.AddHours(1),
                signingCredentials: ...)
            );

After your token is created and sent, validate your incoming request based on your tastes (checking time, user's data, issuer).

ASP.NET Core JWT Bearer Token Custom Validation

Creating RESTful API with Authentication

EDIT: Using Xamarin and Visual Studio on the same machine, didn't gave me this kind of problems but in that case, I was using Visual Studio Emulator. You could give it a try and avoid doing other types of workarounds.