The correct approach is using "Accrual" rather than "Cash", this is based on the tax form design/instruction perspective. This can be verified by the tax form instructions Gross sales means gross sales i.e. invoiced sales.
Note: There is no specification for cash sales.
Same for cost of sales. Note the special provision allowing SBE's to not make opening /closing stock adjustments. Once again, no mention of reporting only for cost of sales expensed i.e. cash basis. Also, see reference to normal accounting procedure, which I believe is accruals basis.
The balance sheet facts are clearly accruals based.
And this is telling. STS is the forerunner to SBE. i.e. Small Business Entity. Note the requirement for adjustments in the reconciliation section - Item 7.
And most telling of all - very specific instructions for adjusting debtors & creditors through Item 7 Reconciliation to derive cash basis.
We provide functionality for these adjustments - i.e. User specifies AR + AP, also the GST on these and LodgeIT Auto-calculates the adjustments. Possibly we can get these values in the API response.