Invoice in different currency

My system currency is set to South African Rand (ZAR)
I do receive some invoices in UK £ (GBP)
I have set the currency of those suppliers to GBP, and record the invoces from them in GBP
But when I go to ‘spend money’ the GBP amount is shown as a ZAR amount (not adjusted by exchange rate or anything - if I have £120 in as the amount invoiced to me, when I go to pay it, it shows as 120 ZAR. The currency field is grayed out so I can’t change it there.
I just want to show that I’ve paid £120, with no currency conversion.
How do I do that?

You can only pay in GBP from a bank or cash account denominated in GBP. However, when spending money to pay a GBP purchase invoice from a ZAR bank account, there will be an optional field for the GBP amount (at the far right end of the line item). If you enter the GBP amount there, Manager will interpret the ZAR payment as being equivalent to the GBP invoice, ignoring any other exchange rate that is set.

Be careful, though. Manager does not calculate what the base currency payment should be. It uses the foreign currency number. So you will still need to figure out how much to pay if you are paying in base currency. It may be advantageous to maintain a foreign currency bank account to circumvent such problems.

Thanks, it worked.