I want to give my clients the option to add a monthly service to their package and have the cost reflected in the payment plan. Currently, when the add-on service is selected, the full cost of the add-on is added to the final payment event. I would like to be able to choose how the add-on is applied to the payment plan so that its cost is divided between certain payment events.

I think adding "add-on costs" properties to the payment events module would make this possible. The fields could list the names of the optional add-ons that are included in the package with fields to add the portion of the add-on cost that should be applied to the payment event. Similar to the current "Amount type" and "Amount" fields in the Payment Plan settings.

Also, when the add-on is selected, the payment event's title could update to reflect the addition.