What is the easiest way to add a payment service in developing countries?

Hey guys! My cousin has a bigger clothing shop in a third world country. They do not have paypal or credit cards and cannot use their bank accounts for online banking. Since he gets many requests from europe and the US he asked me if I could help him integrate a payment solution. Unfortunately I do not know how and he does not use smth like shopify where theres a built-in solution. Any ideas on how we could solve this?