User Exit for FB50 Documents posting,

Hi,

User posting Number of document from excel to SAP using GLSU tool. I hope its calling FB50 Tcode while posting in SAP.

I want to write a user exit at document line item level. Kindly give list of user exit available for this.

Requirement is, whenever user enter material number and plant while posting document, system should check whether that material is maintained in that plant or not. If not, give error message.

Regards,

Venkat