Preview not working

Hi,

I was looking for a plugin like this for a long time and now I finally found it.
But…
I set it up properly and I can select different fonts. However, the preview of the default font is working, but when I select a different one, the preview is empty.

Any help is much appreciated.

https://ww.wp.xz.cn/plugins/acf-google-font-selector-field/