Roi and external price files

[melbv]

Hi team
I am just starting to work with hledger which works great for me thus far.
I have a quick issue with the roi command. After the below declaration:

hledger roi -f personal.journal --investment assets:Investments -Q --cost --value=then,"$" --infer-market-price --pnl "unrealized"

I get an error message:

hledger: Amounts could not be converted to a single cost basis

I am using a separate .prices file for ease of data management which works a charm with commands like 'bs' or 'is' but does not seem to work with 'roi'.
My declaration of the price file is:

include personal.prices

Is this a known issue or is there a declaration I am not instructing 'roi' properly?
Many thanks in advance
M

My config below:

hledger 1.22.2, mac-x86_64