Google restricts FCM service based on IP Address, Is there any other free Android push notification provider?

I start to write down a simple push notification App using FCM For Android. But I got this message in my Android studio Log.

signInWithCustomToken com.google.firebase.FirebaseException: An internal error has occurred. [ This service is not available from Iran. If you believe the country of origin was incorrectly identified, please report it at https://support.google.com/websearch/contact/ip. ]

My Android (client) app works fine[Successful Registering and Signing In and Receiving notification] when I use with VPN to change my IP.

My question: is there any way to use FCM for my project beside forcing customers to use VPN? If not what are other alternatives for FCM that provides free and pay as you go service for cross-platform push Notification?[it is clear that companies that uses FCM/GCM services as 3rd party like Batch.com, Backendless, Pushwoosh wouldn't do any help]

by free, i mean for small amount of users (around 1000 MAU)

EDIT: As Antoine Guénard said, with batch my app registered and got Token and authenticated without any problem but receives test notification only through VPN.

The exception occurred while calling signInWithCustomToken which is related to the Firebase Authentication feature, not Firebase Cloud Messaging (FCM).

We at Batch.com have many customers in Iran as we are based in Europe not US and most of the business sanctions were lifted last year. Our webservices are not geo-restricted like Firebase ones so I don't see a reason why it would fail with us.

On Android, Batch uses Google Cloud Messaging (GCM) through Google Play Services SDK and our Iranian end-users are fully able to subscribe to push notifications and receive those. FCM is basically just a rebranding of GCM, sending APIs works the same, but subscribing from the client side requires another SDK that heavily relies on the Firebase ecosystem.

Edit: from Firebase term of services: