hello @KKL1 thanks for your post. If you go to your Customer Directory in your Square Dashboard (assuming you know the customer's name), you may be able to find that customer, and then click on "Message" and send your note to your customer. This may not be an option however if that customer opted-out of contact from stores, and you don't have a direct email address for them.
Is this an explanation that the customer needs to see...or if you are talking about just making a note for your own reference, you can do this in their customer profile in the notes field.
