The "DeviceTokenNotForTopic" error typically indicates a mismatch between your app’s bundle ID, VoIP certificate, or APNs environment (sandbox vs. production). Start by verifying that the VoIP certificate in the Apple Developer Portal matches your app’s bundle ID exactly and that you’re using a VoIP Services Certificate, not a standard push certificate. Ensure the environment aligns with your certificate type: use the sandbox endpoint (api.sandbox.push.apple.com) for development and the production endpoint (api.push.apple.com) for live use. Double-check that the device token you’re using comes from PKPushRegistry for VoIP pushes and matches your app’s bundle ID without any formatting errors. Test your certificate by exporting it as .p12, converting it to .pem with openssl, and using tools like PushTry or curl to send test notifications. If you resolved trust issues with your Keychain certificate, confirm it’s now fully trusted and re-export the .pem file if needed. If problems persist, consider deleting and recreating the VoIP certificate in the Developer Portal, then updating your server with the new certificate. Also, review APNs logs in the macOS Console app or your server logs for more details. Finally, if all else fails, reach out to Apple Developer Support with detailed information about the issue and the steps you’ve taken to resolve it.