When trying to purchase the subscription or make any other in-app purchases in the ABBYY applications, the following error messages appear: "Cannot connect to iTunes Store." and  "In-app purchases are not allowed.".

These messages indicate that in-app purchases are not allowed on your device.

Solution

1. Close all background applications;
2. Go to Settings > Screen Time;
3. Tap on Content & Privacy Restrictions;
4. Turn on Content & Privacy Restrictions and tap on iTunes & App Store Purchases;
5. Allow In-app Purchases;
6. Restart your device;
7. Try to purchase the subscription.