@Diego554 You can also try messaging the guest saying something like "Hi XX, as you can see from the house rules in my listing info, I don't accept pets, sorry. I'd advise you to withdraw this request so you'll be free to find another listing that cn accommodate your needs."
That may prompt them to withdraw it, and if they don't, you'll have to decline before the 24 hours runs out.
I assume you're aware of the difference between an Inquiry and a Booking Request? If the guest communication comes in the form of an Inquiry, rather than a Request, all you have to do is message back. You don't have to either pre-approve or decline an Inquiry and you can safely ignore the prodding messages from Airbnb to do so. There are no penalties associated with simply messaging back to an Inquiry without clicking on anything.