Mailchimp form dropdown multiple choices

Hello,

I did a dropdown menu with enabled the multiple choices with contact form 7 in WP.
I create the dropdown menu in mailchimp list form and I connected all with the mailchimp plugin.
It’s all ok if I select only one choice (the informations go to the mailchimp list). But if I select more than one choice in the form it fail, and i receive an error email.

Where is the error?
I mean the dropdown set in mailchimp want only one choices, but I don’t know what I need to set. If I set a checkbox field in mailchimp I don’t see it in mailchimp plugin.
Thank you very much

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