What do I enter for "Gross receipts for section 448 (c)"?

After nearly completing my return, Turbo Tax Business discovered a single error. 

The error took me to Form 1065 P4-5, Under line-item 20E, it wanted me to enter a value for "AG - Gross receipts for section 448 (c)". What do I enter? I never had to do this before. Thank you.