@Salome7
I assume you had a booking request rather than an inquiry. In this case guests are ready to book and have given their credit card details to airbnb. airbnb puts a hold on their card to speed up the process. The hold will be lifted, but it can take some days.
Better keep your calendar up to date so this does not happen again. It is very dispiriting for potential guests to get a decline when they have found available accomodation that they like, then are declined upon. It can put them off booking with airbnb and this will backfire on us hosts. Try putting yourself in their shoes.