You cannot change the primary email address of a SmartFlow site
If SmartFlow shows the Error error message when you try to change the primary email address of a SmartFlow site, do these troubleshooting steps.
A different SmartFlow site uses the same email address
A user account of the SmartFlow site uses the same email address
Use a different email address
You cannot use an email address as the primary email address for more than one SmartFlow site. You must use a different email address.