Under Making Tax Digital your VAT periods come from HMRC: once connected, Tax Optimiser pulls down your open and completed periods (HMRC calls them obligations) and you submit against them — you never type in period dates yourself. Every new organisation starts in demo mode, a safe sandbox where you can practise the whole journey without anything being sent to HMRC.
Connect in demo mode
Open VAT → VAT Returns. While you are in demo mode a banner reminds you that nothing will be sent to HMRC. Click Connect to HMRC DEMO MODE.
Walk the dummy gateway
You'll step through a simulation of HMRC's real connection flow, so there are no surprises when you do it for real: press Continue, then Sign in on the dummy login (no credentials needed in demo mode), and finally Grant authority — this is the permission that lets Tax Optimiser fetch your periods and submit returns on your behalf.
Your VAT periods arrive
Back on VAT Returns you'll see demo periods in the returns table — one already Fulfilled (a completed return can't be submitted against) and one Open awaiting data. The Liabilities and Payments tabs sit alongside. In demo mode you can reset this sample data at any time with Actions → Reset Test Data.
Going live
When you're ready, click the link in the demo banner. The Live mode confirmation reminds you of the one prerequisite: your business must already be signed up to Making Tax Digital with HMRC (you'll have had a confirmation email from them).
In live mode you connect exactly as you practised, but on HMRC's real gateway with your real Government Gateway credentials — HMRC may also ask you to complete two-factor authentication. Accountants can instead connect using their HMRC agent account and submit for every client from one authority. The authority lasts 18 months; when it expires, reconnect from Actions → Reconnect to HMRC. Your live periods then replace the demo ones, and if a period you're expecting hasn't appeared yet, use Refresh data.
Next: Upload your VAT figures.