Free goods for 3rd-party Sale

Dear All,

I have created a 3rd-party order in SAP, it has two items as screen shot:

This SO has the same material code: Item 10 for sale, item 20 for free

for free item (20) set schedule line ""CS"

once, i create Purchase order reference PR, there's message pop up for item 20

How to solve this issue?

Thanks,

Rtn