Is automatic and instant currency conversion via an electronic payment gateway, which does not involve a traditional exchange board, considered usury (riba) or legally dubious?

The e-payment gateway acts as an agent for its customers. If it exchanges currency through another bank, there is no issue, because agency in currency exchange is permissible by scholarly consensus. However, if it exchanges currency itself on behalf of the customer, this involves the unifier of the one who receives and the one who gives, which is prohibited by many scholars. Nevertheless, the Hanbalis permitted it even in currency exchange. Therefore, there is no harm in the gateway exchanging currency itself with the customer's permission.