import RingCentral from '@rc-ex/core';
import PubNubExtension from '@rc-ex/pubnub';

const rc = new RingCentral(...);
const pubNubExtension = new PubNubExtension();
await rc.installExtension(pubNubExtension);

const subscription = await pubNubExtension.subscribe(
    ['/restapi/v1.0/account/~/extension/~/message-store'],
    message => {
       ...
    }
);