Domestic sales in the UK

At what exchange rate should I convert a domestic invoice issued in the UK? Invoice issued in USD with VAT included. Is it possible to convert VAT at the exchange rate from the European Central Bank (ECB)?

See here for VAT https://www.gov.uk/guidance/foreign-currency-transactions-vat-and-tour-operators See here for general accounting purposes https://www.gov.uk/hmrc-internal-manuals/business-income-manual/bim39510

Hi DOROTA1972,
Please see section 7.6 of the following guidance :
VAT guide (VAT Notice 700) 7. Introduction to output tax
Thank you.