Making a custom field as mandatory in billing document cancellation

Dear experts,

How can I make a custom field as mandatory in billing document cancellation (transaction, VF11)?

I have implemented the BAdI, SD_CIN_LV60AU02 - and in there, I have added a statement issuing an error message if a certain condition is met, as follows:-

MESSAGE text-e01 TYPE 'E'.

However, when I tested this out in the transaction, VF11, the billing document items disappear at one point -- this is not expected. I think it's because the MESSAGE statement is not anticipated / expected in the BAdI, SD_CIN_LV60AU02 framework.

How can I implement a better solution for such a requirement?