Defines the structure of a plan changeset.

• :first_interval_starts which is the start date of the first interval for the new plan

• :first_billing_amount is the amount to be billed, net of any credit, at the :first_interval_starts

• :next_interval_starts is the start date of the next interval after the first interval including any credit_days_applied

• :credit_amount is the amount of unconsumed credit of the current plan

• :credit_amount_applied is the amount of credit applied to the new plan. If the :prorate option is :price (the default) the :first_billing_amount is the plan :price reduced by the :credit_amount_applied. If the :prorate option is :period then the :first_billing_amount is the plan price and the :next_interval_date is extended by the :credit_days_applied instead.

• :credit_days_applied is the number of days credit applied to the first interval by adding days to the :first_interval_starts date.

• :credit_period_ends is the date on which any applied credit is consumed or nil

• :carry_forward is any amount of credit carried forward to a subsequent period. If non-zero this amount is a negative Money.t. It is non-zero when the credit amount for the current plan is greater than the price of the new plan. In this case the :first_billing_amount is zero.