Pay Voucher In Alternative Currency

Hello,

I have matched the receipt (Euro) and then raise the voucher but I wanted to alter the voucher to USD and was unable to do so, the GL Account is non-monetary so it was my understanding I could change the currency on the voucher? When I did try to change the voucher to USD I could not find my receipt understandably. But ultimately we want to use the multi-bank function and pay our suppliers in USD or GBP Or EUR etc.