On th Right hand side of the VAT page it says to contact HMRC

Hello and Welcome to the Community, accounts-lucidfs 👋

There can be a few reasons why you may see this message on your taxes screen. Have you previously submitted VAT via MTD in QuickBooks or will this be your first return?

Are you submitting for your own company or as an accountant on behalf of a client?

Please also check that you have entered the VAT registration number correctly within the settings (Taxes > Edit VAT > Edit Settings), this should be formatted in numbers only without spaces.

Thanks!