This fully stand-alone module adds the payment method 'cash' to your shop. This is very useful if customers order online but then come to your place in order to pick up the purchased products. "Cash" payment will only be available if "Pickup" was selected as shipping method. On top of that, it will be only shown to particular customer groups which can be selected in the admin.
It is easily configurable (see pictures), e.g. you can set the Geo Zone in which it should work.
This module doesn't modify any core OpenCart files.