AR Transaction: Auto Populate Account Segment in DFF field

Hi Gurus,

Your help very much appreciated.

I want to default an account segment in a DFF field.

I have setup a DFF in Line Distribution Information with a SQL Statement : select substr (:TACC_ACC_ASSGN.ACCOUNTING_FLEX,16,7) from dual

I have account value like this 1871-0000-7101-1500061-1111-00000-0000-000

However, when I create a new transaction using existing memo line, the account 1500061 does not populate in the DFF. I want this DFF to have 1500061 automatically upon saving. How can I achieve that?

Thank you very much for all the support.