Hi paddyr , whenever a transaction is posted to AccountRight, the date supplied as the transaction date determines the period in which it is reported. So an invoice date of 15/7/23 can only be reported in the July 2023 period, not any other period, regardless of when it was posted.
If a period is locked when a transaction in that period is posted, the API will reject that transaction. Unlikely, but WB may have processes to overcome that, which might include amending the invoice date to the current month. (I hope you will post their comments).
So AccountRight never in itself takes the date on which it is transacted as the invoice date. And there is only a single date field.