Hi Vicki2
If you would like the note on the payslip you would use the above process and include that in the memo field in the Process Payroll window, which, in turn, would add that message to the payslip.
If you are referring to the actual email message that accompanies the payslip you want to use add that message when in the Print/Email Pay Slips window. Note: Adding that message to the message field would only showcase that message to the first listed email. If you are needing to send that one-off message on all email messages that you are sending, you to want to send those emails individually updating the message as you go.