It is a column of “What is your PayPal ID?” In the item “Manage Payments”.
I’d like to set up a merchant ID, but apparently I only accept email.
The error message is "The email or merchant ID specified is invalid."
I hope to be able to use the merchant ID to prevent spam from coming.
After entering an invalid email address to confirm, it seems that it is done only judging whether it is a mail address because it was able to save without any problem.