Refunding a guest

Hi all! I have a guest that I agreed to refund 100% (they have stayed with me in the past and also I had other reasons). I issued a refund of my full earnings, but the guest has now contacted me (about two weeks later) and it looks like they are missing $20. Logic tells me that this is due to airbnb fees, since I wasn’t paid an extra $20. I explained this to airbnb support, and they were totally unhelpful - they told me to tell the guest to contact support. The guest contacted support, and they were instructed to request the money from me because my policy is strict cancelation (never mind the fact that I have already refunded the entirety of my earnings from the cancelled booking). Has anyone else had a similar problem? I would literally be paying out if my own pocket for this cancellation if that was the case.

Did they pay in the same currency as your listing.

I have seen this before (with smaller amounts) with guests paying in a different currency, where they paid and X amount and after several months they got a refund which was lower than the original sum because the exchange rate changed.

Yes, it was the same currency.

Guest finally got a response from airbnb stating it’s a technical error and that they will refund it.

But I did some research - as a guest, apparently airbnb can withhold your fees if your host has a back to back booking.

Possibly algorithmic suspicion of canceling, and re-booking privately, to avoid the service fee.

Decline their request for $20, that is ridiculous.