Billing cycle — developer's obligations

The developer should submit a charge in every billing cycle, in accordance with current service usage.
The end date of the current cycle (and thus the deadline by which the charge can still be updated) is returned by the next_invoice_day field.
After the trial ends, in the first paid pay as you go cycle, the charge should be submitted the same way as in every subsequent cycle — it will be billed at the end of that cycle.
In the case of an advanced price list with "packages", it is worth submitting the charge for a given package on the first day of the billing cycle. This will help avoid the merchant optionally changing the limit to a lower one — of course, provided that a lower package has not been selected by the merchant in the application interface.