Aria's service credits feature allows you to apply credits to a selection of plans and services and configure credits to expire after a specific period of time to limit their liability. If applied to multiple plans (both master plans and supplemental plans) and services, the credit may be allocated proportionately, based on the percentage of each applicable line item total, with respect to the total of all eligible charges.
The Proportional allocation of service credits parameter governs whether to proportionally allocate credits across all eligible service charges (including surcharge). This parameter is set to False by default, which means that credits apply to invoice line items FIFO (First In First Out), and not proportionately across all eligible service charges. The Proportional allocation of service credits parameter can be set by navigating to Configuration > Billing > Invoice Settings.
You can also assign multiple plans and services to a service credit and set an expiration date via the create_advanced_service_credit API.