Forms Personalization to prevent a pipe ('|') in the invoice number

I am trying to create a forms personalization to check the invoice_num on AP invoice entry and present a message to the user if it contains a pipe symbol ('|').

Trigger Event: WHEN-VALIDATE-RECORD

Trigger Object: INV_SUM_FOLDER

Processing Mode: 'Only in Enter-QueryMode'

If this is true: :REGEXP_LIKE (INV_SUM_FOLDER.INVOICE_NUM,'\|') then I want to display a message to tell the user to remove the pipe symbol.

I am stumped. Can someone point me in the right direction on this forms personalization?

Thanks,

Nancy