It seems that there was a release like the following on the FCM side.
https://firebase.google.com/support/release-notes/ios#fcm

Since this change was released in v10.4.0 of the Firebase iOS SDK, so long as you use v10.3.0 or earlier in your app, it should not affect you.
You can specify the SDK version during plugin installation.

Thank you for the information.

However, the error suddenly occurred even though there was no particular update, etc. for the already released app.
It might be a bug or something on the FCM side that accompanies that change.
For the time being, I will try to avoid it with "try catch", but if you find out anything new, I would be grateful if you could let me know.

In my case, there is no way to get the FCM token, and everything changed from January 17, and my app has been in production for 2 months, and it just broke, since notifications are an important part of the app, I do not allow to log in without there being a token, and just as of yesterday in iOS no new installations log in anymore.

I don't know how to solve obtaining the token, the problem happens no matter what version of FCM I have, the first thing I do when starting the app from 0 is to check if the permissions are there, if they aren't I request them, but this never runs .

@shinwenli @dpa99c Have you found any solution to the problem?

@adirgan As I already wrote, the interim workaround in my case was to catch the error that occurred in "window.FirebasePlugin.getToken" with "trycatch" and call "window.FirebasePlugin.getToken" again .
Is it not available in your environment?

@shinwenli The same error keeps happening, apparently I have to get the APN token first before initializing the firebase autoStart

I'm trying to see how I can fix it

@adirgan I'm sorry I can't help you.
I don't know if it's useful, but in my environment, there were cases where an error did not occur if an alert screen was displayed with "alert(1);" etc. before calling "getToken".
I'd like to do some more research myself.

@shinwenli My problem is that I need push notifications, and I still can't find a way to obtain the token

@adirgan In my case, the modal message to get permission for notifications was showing and then (after allowing notifications) I was getting an error.
Once the app was closed due to an error, the next time it was launched, it already had the authority (the token was issued), so restarting the app could avoid the problem.
If you look at the debug log in XCode, can't you get the token itself?

@shinwenli I'm looking at what the correct order is, if first ask for permission, and then try to get the APN token, I'm not sure, the log still doesn't show anything useful

@shinwenli I tell you that I already found the solution, the first thing you have to do is use these 2 functions, hasPermission and grantPermission, if the permission is accepted you use these functions getAPNSToken and onApnsTokenReceived, the last function is an observable, at the moment that this observable gives you return the ios APN token, then you can already get the FCM token without any problem.

And with that everything is solved, you will always get the token, if you have the permission and you have the APN Token first.

Checking the Firabase SDK iOS github, the problem is that they changed the Firebase backend API, and the API no longer accepts saving an FCM token without which the APN is created first, therefore you always have to verify that have the permissions and request the APN token before requesting the FCM Token

Earlier, when I started the app that had the error (no countermeasures were taken), it was confirmed that it started normally.
Perhaps it was a bug on the FCM side and FCM fixed it.

@dpa99c @adirgan Thank you for all the information.
This solved the issue that I was having trouble with.

@shinwenli Yes, it is indeed a problem that FCM originated, but for them it is not a bug, and what they want, according to what I see on github, is that in their DB there are no FCM Tokens without APN Tokens, and that is why now it is mandatory that the APN always be there. token first

@adirgan That information is very informative for me. I thought that "getToken()" was the flow of processing to get even the APNs token. So, does Firebase currently send push notifications from FCM without APNs tokens?
Thank you, I will learn a lot.

@shinwenli It was like that until 2 days ago, but with this change in the SDK API, it is no longer possible to do that, now you always have to obtain the APN Token first and then use getToken()

Before when I let you create the FCM Token without the APN, a notification would never arrive to that phone, but before when you used the getToken() after requesting the notification permission it was automatic that it created the APN, now you just have to do the logic complete oneself

@adirgan With the latest SDK released the other day, I was able to learn that it is necessary to acquire APNs first as you said.
Even the latest SDK can be handled by using firebasex's "getAPNSToken" and "onApnsTokenReceived", so I think this is very important information. thank you.

@shinwenli Right now doing tests, apparently they put it back as before, that is, if you have an older version of SDK FCM than 10.4.0, you can continue working with getToken(), they just changed it about 20 minutes ago, but I think it's important work as I told you before and update to version 10.4.0, so as not to have problems in the future.

firebase/firebase-ios-sdk#10679

the last comment indicated that they made a pullback of the changes made to the server