FI - Valuation

Hi

I need a little help with a requirement, I have a trans FB60 enter vendor invoice, In the reference field the put a tracking number. The requirement is when they enter the tracking number in the reference field and it is identical to the vendor which is possible. They want a pop up warning. I tried to create a validation but in the table GB01 the field BSEG-LIFNR is set to exclude. Is there any way around this

Thanks