We had to integrate the solution of our bank (see https://paiement.systempay.fr/doc/en-EN/form-payment/quick-start-guide/sitemap.html https://paiement.systempay

We had to integrate the solution of our bank (see https://paiement.systempay.fr/doc/en-EN/form-payment/quick-start-guide/sitemap.html https://paiement.systempay.fr/doc/en-EN/form-payment/quick-s...), which was not very complicated since it's basically just a form, a hmac signature and a return URL.