I ran into an issue today with gifting my kids some games. They got a Steam Deck each for Christmas, so I purchased some games on my parental account and gifted them each 6 games.

They are in my steam family as children. When I tried to view the gifts on the kids accounts it would tell me they need to request permission which I accepted on their accounts, then I could see the gifts to accept or decline.

When clicking Accept I'd receive the error in the title. If I tried to decline the gift it'd just spin and never finish loading.

After much trying, I realised I had to disable the "Allow access to their online profile, screenshots and achievements" and "Allow access the steam store" restrictions for it to allow the account to accept the gifts.

My guess is the Gift area falls under the 'Allow access to their online profile, screenshots and achievements' and the gift accepting falls under the "Allow access to the steam store" permission, but the Steam App does not prompt for the second permission, so it just presents a useless error.

I got mine sorted so I'm posting this in case someone else is having the same issue this helps them.