Enhancement in va01 while saving

Hello Experts,

I need to validate the fields bill-to-party, Ship-to-party,Payer field in the header data for a particular sold-to-party.

This validation must commence when click on the save button during va01 transaction which will lead to creation of thr order.

I know thw code for validation, But i need to know the exit where i can place my code

ihave already tried exits

USEREXIT_MOVE_FIELD_TO_VBAP

and

USEREXIT_SAVE_DOCUMENT_PREPARE.

but not working, Can you please help me with the wright user - exits.

Thanks,

Satish