@Anna-Karenina0 First of all, those aren't requests, they are inquiries. You never have to decline an Inquiry, and you shouldn't because it lowers your acceptance rate and Airbnb will send you warnings of suspension for too many declines. Just answering the guest within 24 hours, as you did, is all that's required for an Inquiry. If it's a booking request, then you do have to either accept or decline within 24 hours.
Have you tried clearing your cache? That usually makes those dashboard notices disappear if it's been over 24 hours since the inquiry was sent.