About push notification backend

I’m Japanese, so I’m posting a Google translation of Japanese, so the text may be strange, but please forgive me.
I’m creating a backend with bubble.io and a frontend with appgyber.
I used backendless to send push notifications, but for some reason I can’t.
We are verifying the problem, but it may not be fixed.
I can’t program, so any push notification using the REST API is fine, but is there any other recommended app?