I'm creating an React native app and I'm trying to send push notifications to my iOS users with FCM. My first tests weren't very successful because I always had the error "Requested entity was not found" so I thought that I had a configuration issue. The weird thing is that some hours later, a script that send programmatically push notifications to my users has been launched and I noticed that all my iOS users received the push notification. So I made other tests to understand what happened and actually, I have come to the conclusion that tokens for iOS users are taking time to start working. For each test that I made, I have allowed push notification on the iOS phone, then right after the token generation, I tried to send push notification and I got "Requested entity was not found". Then some hours laters (I couldn't tell specific time), I tried again and this time, push notification was send and since today, phones that have allowed push notification are still receiving push notification without any problem.
I've read lot of APNS and FCM documentation but none of them wrote about time before token validation/activation so I don't really know what to think. Do you have any idea ?