Hi, i see that your path for image go to:
plugins/wp-favorite-posts/img/heart.png
But in reality your folder is “wp-favorite-posts-extended”
the url should be: plugins/wp-favorite-posts-extended/img/heart.png

I just renamed the folder to wp-favorite-posts and remove the -extended to fix it.

https://wordpress.org/plugins/wp-favorite-posts-extended/