Conditional logic on checkbox activation

I purchased the MailChimp extension for Ultimate Member, and would like to add a text box field with a conditional logic, to make it visible if the user enables the mailchimp checkbox.

What rule do I need to choose for the conditional logic of the text box? The drop-down list only shows these values:
– empty
– not empty
– equals to
– not equals
– greater than
– less than
– contains

Thank you for any hint 👍</img>