The transaction fees are as follows:
For the PayPal payment method: 2.9% + €0.35
For credit and debit cards: 1.2% + €0.35
For American Express cards (coming soon): 3.5% + €0.35
For cross-border purchases, add 0.5% for all transactions within the Euro zone and 2% for transactions with other countries.
These fees are also displayed here: https://www.prestashop.com/fr/prestashopcheckout