May be I have this wrong, however when selling other business products B2B on shopify, both the supplier and the retailer if registered are paying VAT on the same total selling price of the sale. The collective credit, paid from retailer to supplier, should be classed as an expense with VAT, so that VAT can be claimed back and then the supplier pays the majority of the VAT on the sale and the retailer only the VAT on the profit. Of course UK VAT rules want an invoice with a VAT number - ? should that be a shopify invoice for all collective credits may be?