Nothing works at all. No preview, no test mails

Hello – I installed Kadence to overhaul my WooCommerce emails – but: Nothing seems to work. When I start the email customizer, the preview area remains blank (see: https://www.baylands.org/kadence-no-preview.png). The tab header keeps saying, “Customize: Loading…”.
Also, whatever I do, I cannot send test emails to maybe see what I can’t see in the preview: I just get an error see here – https://www.baylands.org/kadence-mail-fail.png even though my site sends mails all the time.

What is going wrong?

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