The site owner needed to launch an online payment solution that allowed them to send simple links to clients to pay for services rendered. We could not use a standard shopping cart, since the amount due is not fixed and payment plans are negotiated per client.
The client needed to accept the two different types of payment structure: a one-time payment and a multiple-installment repayment over time with a user-defined amount and repayment schedule. The client had selected the pro version of an existing WordPress plugin, WP Simple Pay. It performed great great except it did not explicitly support our concept of dynamic installment plans.