Introduction
This blog post explains how to send FCM Push notifications as a Firebase admin. There are many Google Firebase tutorials available on the subject, but they often not clear and step-by-step. As such, here is my code, I hope this helps everyone.
1. Add the Firebase admin .net SDK by NuGet
2. Get a Firebase service account key from Project Setting -> Service account -> Click on generate new private key.

3. Initialize the Firebase Admin SDK in startup.cs

  1. /* - - - - - - - - - - FCM Admin SDK - - - - - - - - - - - - - - - - */
  2. public IServiceProvider ConfigureServices(IServiceCollection services)
  3. var googleCredential = _hostingEnvironment.ContentRootPath;
  4. var filePath = Configuration.GetSection("GoogleFirebase")["fileName"];
  5. googleCredential = Path.Combine(googleCredential, filePath);
  6. var credential = GoogleCredential.FromFile(googleCredential);
  7. FirebaseApp.Create(new AppOptions()
  8. {
  10. Credential = credential
  11. });
  12. }

4. Send Notification

  1. public virtual async Task<string> SendNotification(List<string> clientToken, string title, string body)
  2. {
  3. var registrationTokens = clientToken;
  4. var message = new MulticastMessage()
  5. {
  6. Tokens = registrationTokens,
  7. Data = new Dictionary<string, string>()
  8. {
  9. {"title", title},
  10. {"body", body},
  11. },
  12. };
  13. var response = await FirebaseMessaging.DefaultInstance.SendMulticastAsync(message).ConfigureAwait(true);
  14. return "";
  15. }
That's it.