OneSignal exported endpoints cause "VAPID public key mismatch" in Firefox v2 push

[ivptr]

I'm encountering problem delivering push notifications to Firefox using endpoints exported from OneSignal database.

• Notifications sent to endpoints beginning with https://updates.push.services.mozilla.com/wpush/v1/ are working correctly.
• However, endpoints starting with https://updates.push.services.mozilla.com/wpush/v2/ consistently return a 401 Unauthorized error:

{
  "code": 401,
  "errno": 109,
  "error": "Unauthorized",
  "message": "VAPID public key mismatch",
  "more_info": "http://autopush.readthedocs.io/en/latest/http.html#error-codes"
}

Sending to Chrome and Edge works fine using the same VAPID key. OneSignal claims the VAPID key is the same.

Tried disabling automatic padding via setAutomaticPadding(false), but it had no effect.

PHP Web Push example works fine with the same Firefox for Windows v142.0.1.

What am I overlooking?