Version of Zoho Books is just the default one on sign-up from New Zealand.
When I go to settings -> tax, only 'tax rates' is available. No way to switch on GST functionality.
In 'organisation' settings there is no option to switch-on GST functionality.

The key requirement is a report that provides two figures, one the tax on all inputs (purchases) for the period and the other tax on all outputs (sales) for the period. The period needs to be able to be specified (in our case it is 2 months, i.e. every 2 months). The difference is either GST owed to the tax department here, or GST owing by the tax department (so we either pay or get a refund). This amount owed or to be refunded should appear in a GST Payable account or similar, so that payments or refunds balance this to zero for the (2 months in our case) period.

GST transactions for us are cash rather than accrual.

Advice would be appreciated.