Why are there no VAT on Sale or VAT on Cost fields under the Flat Rate Scheme?
In the VAT Settings panel, the Flat Rate VAT scheme, unlike the Standard Rate, has no VAT on Cost or VAT on Sale variables - this is because they are not relevant to this scheme
On the Flat Rate scheme, you will always pay the flat rate percentage (12.30% here) of the Sale Price to the government, and you cannot claim anything back. So VAT on Cost and VAT on Sale are not relevant because you cannot change them.