@DU54 Are you playing on 2 devices or are you sharing your account with anyone?
This occurred because the offer was received a minimum of 10 hours prior to when you tried to accept the offer - but you were navigating through other parts of the game between your last battle and accepting the offer - something that’s not meant to be possible as the offer is only valid for as long as you are on the merchant offer screen. The second you leave that screen either by accepting the offer or by dismissing it, the offer is no longer active or available to you.
So that indicates the game was open on 2 devices and while one had this Angel Offer open, the other device was still playing other areas of the game which deactivated this offer as intended.
@Ant_Man roughly what time (and timezone) did you get an error? Was it a CLIFFY error as well? I don’t suppose you got a screenshot of the error message?