title: SWIFT IOS send OneSignal notification across app
body: <p>My notification works fine when a user is sending a notification to another user in the same app. </p>
  
  <pre><code>let userPushId = order?.pushId
  
      let jsonMessage: [AnyHashable: Any]! = ["contents": ["en": "is taking your order"],
                  "headings": ["en": self.myUserName ?? "Driver"], "include_player_ids": [userPushId],
                  "ios_badgeType": "Increase", "ios_badgeCount": 1]
  
              OneSignal.postNotification(jsonMessage, onSuccess: { _ in
                  print("from\(self.myUserName ?? "") to \(userPushId)")
              }, onFailure: { _ in
  
                  print("Notification could not be delivered")
              })
  </code></pre>
  
  <p>However, when I need to send notification from a Driver (one app) to a user (another app) with the code above, the user won't receive the notification. I believe I need to add rest API Key or OneSignal app id into the code above, but I don't know how. Could anyone tell me what codes I need to add?</p>