Cannot get Firebase Push Notifications to work

[codesmidnobla]

The function below returns the error:

Malformed UTF-8 characters, possibly incorrectly encoded

If I base64 it, I get the following code, which actually is not UTF-8:

+KghdS97

So now I have 2 questions:

1. How should I store this token in a SQLite database?
2. How should I send this token to Firebase FCM? (I use kreait/firebase-php for this)

public function getPushNotificationsToken(): ?string
{
    if (function_exists('nativephp_apns_get_token')) {
        return nativephp_apns_get_token();
    }

    return null;
}