สวัสดี ครับ! (Sawatdee krap!)^^
As for the rebate condition of suppliers, it is more complicated than we had thought.
Therefore I leave up to you whether or not you journalize this income as an accrued income on a monthly basis in accordance with accrual accounting.
And according to the information from Mr. Ota, these rebates will be settled with credit note.
It means gross profit will be fluctuated whenever you journalize this income.
Hence, in order to grasp this income on accounting, I think that the account title should be distinguished between this income and cost of sales.
After making your decision, please kindly let me know how to address it.