A common question users ask is how to add a new payment processor – such as Adyen rather than Stripe or Paypal. It’s fairly easy to do this, here are brief instructions so you know which files to modify

To add a new payment method:
Http/Controllers/Account/BankAccountController.php – to create a new account
Http/Controllers/CheckoutController.php – to confirm the payment

and the associated views
resources/themes/default/listing/widgets/buy_widget.twig – to open the payment widget
resources/themes/default/account/bank_account.twig – so users can add their bank details, account number etc.