Where to implement paybox online payment, on the front or back side?

Question

Payment systems

I was given a task on the sportarea website to add a new feature, "My Cards". When the user is authorized, he will have the opportunity to add his card, because. we are working with the paybox system , they have provided this feature and prepared the documentation here and I wondered where it is more reasonable to do this function on the back or front side?
When connecting from the old front using axios + vuex, they give me an error that paybox does not allow cross-domain requests, and with the no-cors method, paybox does not respond to requests at all, what should I do? MB to tell the back to make it at home, and after that I will simply display it from the client via api