Until recently, many ticketing platforms let organisers choose: absorb the card fee, or pass it on to the buyer at checkout. For card payments by consumers in the UK and Ireland, passing it on is not allowed.
What the law says
In the UK, the Consumer Rights (Payment Surcharges) Regulations 2012 (regulation 6A, in force since January 2018) stop a seller charging a consumer extra for paying by most cards and similar payment methods. In Ireland, regulation 86(6) of the European Union (Payment Services) Regulations 2018 (S.I. 6/2018) does the same. A card fee added at checkout is exactly that kind of charge.
How tickts handles the card fee
On tickts, the card fee always comes out of the ticket price. Your buyer pays exactly the price you set, and tickts adds no booking fee and takes no commission. The only deduction is Stripe's card fee: 1.5% + 20p for a standard UK card. On a £10 ticket that is 35p, so you receive £9.65.
If you want to receive a set amount
Build the card fee into the ticket price instead. To receive £10 after Stripe's standard UK card fee, set the price at £10.36: Stripe takes 36p and you receive £10. Your buyers see one price, from the event page to the checkout.
This is general information, not legal advice.