Hello, the Firebase Instance ID service is deprecated, and it might not work properly.
Just remove it, and the Device Token might start being rightly filled.
For the Sender ID, on Android, you must set it during the installation process.
It should be like this:
ParseInstallation installation = ParseInstallation.getCurrentInstallation();
installation.put("GCMSenderId", INSERT_YOUR_SENDER_ID);
installation.saveInBackground();
With the snippet above, the GCMSenderId field shall start being filled.
These steps work for all of my Android Studio projects, so, please, let me know if they also work for Xamarin projects.