Starting Live Activity with APNs

I am trying to start a live activity using APNs, but it is not supported with firebase or onesignal, is there any other way to send a PN to the device, I have device token, bundle ID, team ID, and apnsKeyID. I also tried hitting this URL: 'https://api.development.push.apple.com/3/device/{deviceToken}', but it gives an error "unable to set private key file" even though I have given the path to my .pem file that has a private key in it enclosed under BEGIN CERTIFICATE and END CERTIFICATE. It will be great if someone could guide me here

Starting Live Activity with APNs
 
 
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