I am sorry to hear that you are experiencing problems with the Call of Duty App. Please verify your phone version and iOS, and let me know if those are compatible with the App by visiting this link: Activision Support.
We are aware that some players are having issues with the app at the moment. Beachhead is aware of this and are currently working on it. You can find more updates here Beachhead Studio. In the mean time, try relinking your game account to your Call of Duty account as well as relogging into the app.
Try this fix bro:
1. delete the application
2. reboot your device
4. You can unlink and relink your console account there (I am referring to step 3)
5. Download the app and check. Keep updated if it works for you, man!