Hey Mark,
if you're on Android, please make sure that the launcher has the necessary permissions. If they already do, try disabling and re-enabling those permissions again. Deleting and reinstalling the launcher can also help in these situations.
If you're on PC, your download might be corrupted so I'd make sure the download isn't paused or interrupted. Also, some antivirus software can tag the download as a false threat. Allowing/giving necessary access can also help in some situations.
I hope this helps!