The client required a payment system for parking fees whereby the user pays on a monthy basis on a set day of the month using authorize net ARB billing agreements.  However they also required an initial payment to go through within seven days of the requested start of service which was pro-rated to the duration between that start date and the regular payment date. 

This was solved by creating two ARB agreements, one consisting of a single payment on a day within seven days of the start of service and the other a repeating payment on the regular payment date.  All authorize net systems (ARB or CIM) require a transaction to enable a user's credit card to be fully verified, so a mandatory AIM transaction of a nominal value was used which is immediately voided.

Also installed a custom coupon facility.