If the Ernst & Young tax advice which was on the Airbnb website is correct then you do not have to charge VAT. As there is no VAT on a residential letting.
See here
https://www.askaboutmoney.com/threads/airbnb-tax-question.204764/#post-1527072
It is in my opinion, and it seems your accountant agrees with me, that E&Y are wrong. Airbnb income generally is Schedule D income and as such subject to VAT. If your turnover is expected to go over €37,500 you must register for VAT.
Your turnover is not just what you receive from Airbnb it includes the Airbnb fee, the 3%, which they have already deducted from the money they pay you.
You must then account to Revenue for 8.25688 % (that is 9% of the net) of this gross as VAT on sales, you can deduct any VAT on inputs, which include the Airbnb Fee.
Airbnb provide all the information you need, except any costs you have had yourself obviously.