After just testing the SSL Certificate again to connect using APNs using openssl s_client -connect api.sandbox.push.apple.com:443 -cert aps.cer -certform DER -key PushChatKey.pem -keyform PEM and a connections was made.
In the past week, I also used
curl -v --header 'apns-topic: com.faunna.PushChat' --header apns-push-type: alert --cert aps.cer --cert-type DER --key PushChatKey.pem --key-type PEM --data '{"aps":{"alert":"Hello From Faunna"}}' --http2 https://api.sandbox.push.apple.com/3/device/258ecf658e25256c8f06ddb1138d5d536ba0e760a96ebd12d3b1dbe112857c58
To send a test push notification to the test device.
I may submit a TSI to Apple.