how to call web api in another asp.net project

https://learn.microsoft.com/en-us/aspnet/web-api/overview/getting-started-with-aspnet-web-api/using-web-api-with-aspnet-web-forms

calling API from one project (Localhost:1234 or Domain A) to another project (localhost:3456 or DomainB) violates the CORS policy, so first step should be to enable CORS in your API project.

After enabling the CORS you can use HttpClient or RestClient or Jquery Ajax to consume the API from any project.

This is how you can consume API from web forms

To enable CORS in ASP.NET Core API

//inside startup.cs (till .NET 5) or Inside Main() in (.NET 6 and .NET 7)
//inside configure method
app.UseCors("CorsApi");

//inside configureServices method
services.AddCors(options =>
{
    options.AddPolicy("CorsApi",
        builder => builder.AllowAnyOrigin()
            .AllowAnyHeader()
            .AllowAnyMethod());
});

You can use RestSharp which is an open-source HTTP Client library that we can use to consume APIs.

For more details plese check the below articles

https://stackoverflow.com/questions/10226089/restsharp-simple-complete-example

https://code-maze.com/aspnetcore-using-restsharp-consume-api/