Sometimes a premium subscription needs to be reactivated. This can happen after setting up a new device or reinstalling the app.
When this happens the premium features are not available and adverts still appear.
To fix this, use the Restore Purchases option.
On the main Planning screen, tap the (…) button
Tap Upgrade to Premium
Underneath the options to purchase, tap the Restore Purchases link
This will contact Apple’s server’s and re-fetch your subscription details. This will remove adverts and restore your previous settings.