I figured out the iOS Payload notification syntax in this post:

Example of new Firebase HTTP v1 iOS JSON Payload notification syntax

but I get 403 errors on the HttpWebResponse resp = (HttpWebResponse)req.GetResponse();

This only fails on Apple send. Android works fine, and we’ve always gotten by with the same code on both, except for possibly some proj config stuff. Could this have anything to do with the fact that this is a silent notification (“apns-push-type” : “background”) ?