The error strictly indicates that you are using the wrong APNS certificate. It may be expired, or is it just an old type of certificate (created before December 2015).
A year ago, Apple introduced new universal certificates, and today it only supports them. Therefore, you need to create a new universal certificate in order to activate push notifications again.
There is a .p12 extension in the apple.com certificate, you may not be able to convert it.
Another stone that I use to send apns (rpush) notifications can use p12 certificates without any problems. You can also send a test run using the Rpush gem to find out if there is a Houston problem or a certificate problem.
nattfodd
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