Generally, it should be possible to tap on the "Restore" (or "Restore Purchases") button in the app (usually found in Parents' section or Settings) to restore the full content within the app.

If that doesn't help:

Please make sure that you are connected to the App Store and have internet access.

Try logging out of your account and logging back in.

Do you use parental control on your device? Sometimes, this error can happen when it is switched on.

If nothing else helps, we recommend to try deleting the app, restarting the device, and reinstalling the app from the store. Then, using Restore button should help.

Unfortunately, once or twice we've seen that it simply did not work on customer's home wi-fi, but it worked without any problems on a different wi-fi network.