Elementor and Popup Maker conflict

Hi
I tried to edit the content of the popups using the free version of Elementor but I got this error: “The preview could not be loaded”. I followed all the troubleshooting steps suggested by the Elementor support team but I’m still getting the error message.

To be completely sure it’s not a theme or server issue I used two WordPress sites (one in my localhost and another in a hosting service), the Twenty Fifteen themes, and only the last version of Elementor and Popup Maker plugins installed but I keep getting the same error.

How can I solve this?