Setting the value in a table column based on a comparison between two columns one in a ref table

[21agdgcf]

Hi

I have two tables ,Ledger and a ref table supplier, in the ledger table I have a "Counterpary" column that I am comparing with a Supplier Business name if they match then I am inserting the row id in the ref column of the ledger table using a bot

I have tried this logic in a virtual field to test but am missing something

if([_THISROW].[Counter Party]= [Supplier].[Business Name],[Supplier].[Business Name],"Not Known")

all help appreciated

Thanks

A