I upgraded to premium via AppStore. It works on the web app but not on my iPhone or ipad. Why is this? Do I need to buy premium for every device?
You don't have to buy Premium for each device, Premium is an account-based upgrade.
There are two reasons why you may not see Premium features on iOS:
1. You haven't logged out and back into the iOS app and it still thinks the account is free.
2. You're logging into a different account on iOS than on the web.
Thanks. It started working a couple of hours later. Maybe a slow sync or similar.