Tax and GST reports
GST collected and paid for a period, in a form suited to your BAS.
GST is calculated per line on the discounted net and stored on each invoice, so the tax on a document is a recorded figure rather than one re-derived later.
Whether a document was issued as a tax invoice is recorded on the invoice itself. That stays correct even if your GST registration changes afterwards.
For a period figure, run the GST / BAS report in Reports. It gives G1 total sales and 1A GST on sales for a BAS quarter or any range you pick, with refunds taken off at the original sale's own GST rate. It is admin only, and it is the sales side only — there is no purchases ledger in the platform, so 1B is not derived.
This describes how the software calculates and stores GST, not how to complete your BAS.