Hi Joans,
This is a common issue in AFS.
If invoices for AFS-materials are created by collective processing, differences between invoice quantity (VBRP-FKIMG) and pricing quantity (KONV-KAWRT) can occur. The result is a incorrect price calculation for the concerned billing item.
You can try to run report J_3AINQT. You can cancel the documents and then try to recreate the same.
Thanks
Ashish