In order to send push notifications via the Google and Apple push servers, IAM must be able to connect to the push servers. Make sure that the local firewall is configured accordingly, or configure a proxy.
For iOS:
api.push.apple.com:443
must be reachable- for sandbox mode,
api.development.push.apple.com:443
must be reachable
For Android:
fcm.googleapis.com
must be reachable
Note that the Java code from the Vasco library must be able to resolve these hostnames.