NextGEN featured image does not work

Hello,
I just installed NextGEN and now I can’t get any featured images on my webpages.
I am also not able to get the normal featured images either.
When I click on Set NextGEN featured image, I go down to the bottom, select my gallery, then click on the image in the gallery. I don’t fill anything out and click on the link that says use as featured image. I then click on the save all button. I then click publish. When I go to my webpage, nothing shows up.
I sometimes get an error that says that I can’t use that image, then I think I need to clear the current image.
But it still doesn’t show.

https://ww.wp.xz.cn/plugins/nextgen-gallery/