Generally, "Unverified check-ins" error is displayed when a guest tries to redeem his/her "Redeemable card (Base redeemable)" even when there are one or more pending check-ins in their account.
The settings for the Pending Check-ins can be found under:
Cockpit > Earning > Checkin Update > Receipt Update Delay Minutes
For example, "Receipt Update Delay Minutes" is set to 5 minutes. So, if a user will try to redeem his/her "Redeemable card" within 5 minutes of the 10th check-in (final check-in to earn a redeemable reward) done, this error will be displayed.