Unearned Revenue Account is not accepting a simple sql based rule to be used

Our COA has a profit center segment which is not marked with any flex-field qualifier.  At the project task level we capture the profit center in a DFF.

We have created a rule to populate the profit center segment through a simple sql code which will pick up the profit center GL code from attribute1 of PA_Task table.

However when I am trying to attach the sql based rule into AA assign rule for Unearned Revenue Account, the LOV is not pulling up or showing up the Sql based rule .

The assignment only allowing to save look up set or constant value based rule ,