When I attempt to tag this customer through the partner portal, the Check Availability step first indicates the email is available, but on submission returns this error:
"This user does not have account in this service or this user is not an admin. Please ask this user to login in this service at least once or if the user is not an admin, please convert to admin user."

What I have already tried:
1. Setting password via accounts.zoho.com (blocked by OTP to unknown destination)
2. Logging in at mail.zoho.com (no password available)
3. Logging in at workplace.zoho.com (same OTP block)
4. Partner tagging via the partner portal (returns the error above)