SolvedVCONST24600 | DIY builders and converters VAT Refund Scheme - eligibility of claims: condition 10: have the correct supporting documents been furnished?
From HM Revenue & Customs · VAT Construction
A checklist of required documents is provided in DIY guidance at:
VAT refunds for new builds if you're a DIY housebuilder - Making your claim
VAT refunds for conversions if you're a DIY housebuilder - Making your claim