IOS Firebase messages do not work for custom segments

Question

I have been using Firebase Messaging (sent via the Firebase panel) for several months through several projects without problems, and I LOVE it, however last week I had a problem when I cannot receive notifications in order to switch to iOS for user segments for new projects. If it were just one project, I would suggest that I set something up incorrectly, but I am in the third round and still have problems.

I created p12 files, and even received FCM registration IDs and successfully sent notifications to specific devices, but when I target the user segment for iOS, push notifications never pass.

I would be very grateful if anyone had feedback on this topic. There is not much to say, since I successfully receive notifications on certain devices, so I think this should mean that everything is correctly configured with APNS (although I am VERY open to hear someone let me know that I am mistaken in this assumption).

Thank!