Mysql Does Not Permit Users To Purchase Multiple Accounts

I want to permit MULTIPLE accounts for members.

My site currently does not permit members to have more that one account.

I want to change this to PERMIT multiple accounts.
Accounts are based on the users email address.
When a duplicate email address is input. I get this response…
“Duplicate entry ‘[email protected]’ for key 2”

Code snipit from my database;
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“”PRIMARY KE…