Add payment to completed orders

Suppose an order completed with "pending payment" status.

A user can add a payment method in /user/{userId}/payment-methods
Then admin can apply a payment using that new payment method to a specific order using /admin/commerce/orders/{orderId}/payments/add

but since that route is an admin page, there seems to have no route for authenticated user to apply newly added payment method to pay balance on order.

Is there another route I'm not aware of that could be access by user ?
Would I need to create a custom form for this (that would pratically be the same as /admin/commerce/orders/{orderId}/payments/add but on a different route) or is there a module or a config I'm missing ?