Default value is not appearing in DFF in Payables

Created a context based DFF to capture the information. By default, it should show a value, example, "DefA" and it is an LOV based, DefA and DefB are two values. By default, DFF should have value "DefA". When the users select DefB in the DFF, another field will be populated to capture more information.

I am able to create this DFF under AP_Invoice_Lines, but the only issue is, the default is not coming by default. The user can go and select DefA or DefB.

if DefB is selected, the field is getting populated.

But by default, DefA is not coming in DFF. What could be the reason.