Hello and Welcome to the Community, DUNCAN BOYD!
You can enter a bill and then leave this open and unpaid until you pay this at a later date; if you're using the Standard VAT accounting scheme the VAT on the invoice will be accounted for on your return when you raise the bill (bill date), if you're using the Cash VAT accounting scheme the VAT will be accounted for when you apply the payment (payment date). You can see which scheme you have this set to currently by going to Taxes > Edit VAT > Edit settings.
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