Fatal error: Cannot redeclare class mailchimp in Mailchimp.php on line 19

Hello Dear WPMUDev staff
I just installed the MailChimp Integration plugin but can access the settings.
I'm getting below error message on a blank screen:
Fatal error: Cannot redeclare class mailchimp in /??????/????????/public_html/wp-content/plugins/mailchimp-sync/mailchimp-api/Mailchimp.php on line 19

How can I solve this issue?

Thank you for your help.

Best regards.

Jose