UDF in ORCT

Does anyone know how to add and update a UDF in the ORCT table?

I think B1 stores the header info for all payments in the ORCT table. I would like to tag all incoming payment transactions with a value in a UDF from the "money bag" screen (payment method screen?) My issue is that when I put the udf on the header it is inactive and I cannot activate it. The checkbox to activate the UDF is greyed out.

Thank you,

Rob