To restore your purchase, go to the App Store and ensure you're signed in with the same Apple Account or Google Account you used for the original purchase. Then, reopen Locket, and your purchase should be restored. If its still not working, try the following steps.
Open Locket
Tap your profile photo in the upper right corner
Scroll down to Support
Tap Restore purchases
If the issue continues, please contact Apple or Google Support, as we don’t have control over billing or purchase restorations.