I’d like to add a fixed refundable damage deposit (£100) cost on top of the rate as a fee but I need to have it per accommodation / per stay ( not per day). Is this possible? Am I in the wrong place?
You should simply set the Limit option to “1 day”, so the fee is charged only once per the whole stay: https://prnt.sc/rhuycf. This is how it would look like in the price breakdown: https://prnt.sc/rhuzho.