[ic] Payment on account

[JW]

Hi,
I'm wondering if anyone is using Interchange for accepting payment on
account.  I saw a post alluding to a concept of adding credit to a customer
account through a special product / item.  I can see how this would work if
the special item had a fixed amount, however I would like to set up a
payment item allowing pricing input from the customer.

Any information on how this could be done would be appreciated.

Thanks in advance,
JW