Two Zoho CRM accounts one email address?

Two Zoho CRM accounts one email address?

I'm helping someone incorporate His Zoho Creator app with his Zoho CRM. To do this I registered for my own CRM account to test and learn the system. When he tried to add me as a user to his CRM system he got a message saying my email was already used in another CRM system.

Is it possible to use the same email address on two different CRM systems?

Herb Wexler