VAT at the rate of 20% is still treated as being charged where a supply is made to another VAT registered business, and in this case a VAT invoice must still be issued. what does this mean ? we only need to use flat rate % given in question. so where this 20% came from?
you will use a flat rate scheme to simplify your VAT return process, but your VAT registered costumer doesn’t care which scheme you are using, he only cares where is my vat invoice, i need it to reclaim my input vat. so if you don’t issue it to your costumer, he will not let you go….