Issue MailChimp API adding audience member + Translation pop-up text content

I just bought the plugin and wanted to connect this with MailChimp.
API is connected and the list is found, yet subscribers are only getting listed in the mail list of the plugin, in the WordPress dashboard, and are not showing up in MailChimp audience (no double optin activated).

Another issue is the translation. We work with WPML for translation but the plugin says to use the edit the design in each language (takes you to the Customizer tab of the plugin). Yet, this only works for the source language of the website. When I switch to another language and then try to edit the design, the customizer keeps on loading (in some sort of loop). I tried deactivating all plugins but WPML and this one and the issue persists. Changing from theme Divi to a basic WordPress Theme also gives the same issue.
So I can’t translate the necessary texts in the pop-up for the other languages.