@Marc162 @Sandra856
Marc, like Sandra, I don't recall the Special Offer option with a Reservation Request.
(I've never done Instant Book, so I've been doing Enquiries & Reservation Requests for over 6 years).
In any case, occasionally I've had to deal with the issue you relate, and there is a 4th option of which you seem unaware, namely to contact Customer Services.
Firstly, I message the person sending the Reservation Request informing that Airbnb will not process a booking without the correct numbers, further citing the Host Guarantee won't be applied in this case.. Therefore, I must kindly ask the person to WITHDRAW REQUEST and resubmit with the correct numbers.
If the person is obstinate, fails to reply within a few hours, or replies that I should Decline myself, then I respond by informing that I will phone Airbnb Customer Services to contact the Guest and if necessary cancel the RR.
CS will always do this because they are obligated to uphold T&Cs.
More commonly I have had to apply this technique to 3rd Party Booking Requests.