If you already paid, check the account and subscription before purchasing again. An Unauthorized error on one feature does not by itself mean your payment failed.
Confirm the Memo account email and sign-in method on the device showing the error. Check that it is the same account you used when purchasing.
Open Settings → Subscription and compare the displayed plan with your receipt.
Check whether the receipt is for a Memo web purchase or an App Store subscription.
Check that the subscription is active under iPhone or iPad Settings → your name → Subscriptions. Open Memo with the expected Memo account and use Restore Purchases if available.
Contact support with your account email, receipt or transaction reference, device and app version, screenshot of the displayed plan and the exact error. Say which feature fails and when it happened.
If you already tried restoring purchases, signing out, refreshing or reinstalling, include that. You do not need to repeat those steps while support reviews the account. Do not share passwords, sign-in codes or full card details.