@Dan_Sheila0
Argh.....who persuaded you that 1 nighters were a good idea for such a lovely appartment? It's pretty much an invitation to groups to party and leave. I know that's not much help right now, but consider changing it immediately.
You need to prove damage or additional cleaning fees - or you need to prove more people slept at the property than were booked to do so. 'Say so' is not good enough. Take photos if the place is in a mess, and get a quote for a full clean. Any damage, likewise - but be prepared for a battle.
If you are lucky your guest will admit and pay for extra cleaning if required - if not then it's a claim on the AirBnB platform.
Once you know the 'damage' message your guest and ask for what you think is appropriate - plus if you can prove additional people slept over, then use your 'additional person per night' rate to calculate that. Some people believe you can claim the security deposit just because people had a party - not so - it's for damage/additional cleaning/etc..
Finally - withing 14 days review your guest so that other hosts are not caught out.
Good luck and hope it's not too bad a situation