The proration option is accessible through the Order API, not the Subscription API.

You cannot update the term start date when the proration option is ChargeFullPeriod.

The recurring charge's last billing period must be full when the proration option is ChargeFullPeriod.

When the proration option is ChargeFullPeriod, the billing cycle day must be the term start date, and the billing period must be aligned to the term start date.

You cannot update the recurring charge when the proration option is ChargeFullPeriod.

The suspend date must be the next billing period's start date in the suspend order action.

You can only use this proration option for regular recurring charges. Prepayment charges, discount charges, and delivery pricing charges are not supported.

You cannot overwrite this value from CPQ, but you can still use CPQ to create such subscriptions if the proration option doesn't have to be changed from CPQ.

If the list price base year and the billing period are shorter, the proration option doesn't work.