HMRC first introduced digital processes in 2007 and (as at 1 Jan 2021) has not yet abandoned the use of paper. Some things are only set out on paper, like a VAT reporting cycle!
That means that we need a copy of your VAT Registration Certificate. A form VAT4. HMRC normally posts this about 7-14 days after registration.
It looks a bit like this example and (amongst other things) it tells us if you have a March, June, September, December reporting cycle or some other pattern.