There are two common causes of your purchases being unavailable in Concepts. You can try both of these solutions to see which works for you...

 

Sometimes the Google Play Store app doesn't get a notification of a purchase, causing in-app purchases not to work.

As a fix for this you can clear your Google Play Store data.

1. Close Concepts.
2. Go to Settings > Apps > Google Play Store > Storage > Clear Data.
3. Start the Play Store app before starting up Concepts.

 

When a device is signed into more than one Google account then the Play Store has a bug that causes it to only read purchases from one account. If it chooses the wrong account then your purchase will not show as a available. To fix this:

1. Sign out of the Google accounts that you did NOT use to make the purchase. So that you are only signed into the one that you purchased Concepts with.

2. Run Concepts and check that your purchase is restored.

3. You can now sign back into the other Google accounts.