Cash discount on sales

Hello all,

I would appreciate some help on the following question. Points available.

This issue deals with tcode F-52 (incoming payment). Let's say a customer purchases a product for $299 and has terms of 2% 30 days, net 31. The customer pays in 5 days to take advantage of the discount. Now when I do an F-52, and hit Process Open items, we have the following at the bottom of the system screen:

Amount Entered: $299

Assigned: $293.02

Difference Postings: $5.98

Not assigned :$5.98

When I try to SAVE, I get a message "Difference is too large".

Is there some config I am missing? Also, do I need to Define Accounts for Cash Discount Granted (OBXI)? If I assign an account to OBXI, I'm assuming my discount will go there. Would I then be able to SAVE (post)?