"Exchange rate of gross value is missing" when importing CSV transactions with currency conversions

I’ve been really liking this software, it works very well. But I have had to add transactions manually due to this issue - I have many years of transactions so doing it all manually is very time consuming.

I’m trying to import historical security purchases from CSV. These values are given in GBP, the security is in GBX (*100).

When I try this import, the failure message indicates “Exchange rate of gross value is missing (transaction currency GBP and security currency GBX)”. If I add transactions manually it works fine.

Screenshot of the error (Ignore “transaction does already exist”, that shouldn’t affect this):
image

And the field mapping - I’ve tried mapping currency, gross amount, currency gross amount:
image

I’ve seen a few posts about this from around 2021, which seem to imply this issue was supposed to be fixed after this update: Dividend CSV update but that doesn’t seem to work - Did that only apply to dividends and not transactions (like buying shares?)

Any help will be greatly appreciated.