Message: There was an error loading

Hello!
I’m trying the test version. And I have this error. Screenshot:
https://www.dropbox.com/s/dmhx9r03xi1qp6s/zakeke_error.png

The language of my site is Russian, so my translate for the error text: There was an error loading. Click OK to reload the page.

If I click “OK”: I have this message one more time, and one more, and one more … and so endlessly.

If I close the message (the cross in the top right corner of the message): everything is going well and I can do customising.

Why is this and how to remove the error message?

(my WordPress is 5.4, my WooCommerce is 4.0.1, my Zakeke-plugin is 2.0.13)