Not sending IOS push notifications via gRPC

I am trying to send IOS push notification. It gives success response but gorush docker image throws error.
`goroutine 27 [running]:
github.com/sideshow/apns2.(*Client).Development(...)
/go/pkg/mod/github.com/sideshow/apns2@v0.20.0/client.go:120
github.com/appleboy/gorush/gorush.getApnsClient(...)
/drone/src/gorush/notification_apns.go:356
github.com/appleboy/gorush/gorush.PushToIOS(0x0, 0x0, 0x0, 0x0, 0xc00014c2f0, 0x1, 0x1, 0x1, 0xc0002be480, 0xc, ...)
/drone/src/gorush/notification_apns.go:381 +0x49c
github.com/appleboy/gorush/gorush.SendNotification(0x109c1e0, 0xc00007c570, 0x0, 0x0, 0x0, 0x0, 0xc00014c2f0, 0x1, 0x1, 0x1, ...)
/drone/src/gorush/worker.go:26 +0x107
created by github.com/appleboy/gorush/rpc.(*Server).Send
/drone/src/rpc/server.go:97 +0x513`

Start by reproducing the gRPC Send flow from rpc/server.go, then trace worker.go into getApnsClient and PushToIOS in notification_apns.go. Compare the reported success response with the gorush error and determine what prevents the iOS notification from being delivered. Done means the gRPC request sends an iOS push without the reported error.

Written by the indexing model from the issue text.