Breaking:booking_date (date) is now a required field when creating or updating billing events — affects POST /v1/billing/events and PATCH /v1/billing/events/{id}
Breaking:due_date on InstallmentEvent changed from date-time to date format
Six new billing event types were added to the BillingEvent union: payment, dunning_fee, final_bill, bonus, correction, and custom — clients parsing event responses should handle these new variants
New optional fields were added to all billing event types: direction (debit/credit), status (open/closed), related_event, external_link, attachments, note, and internal_note