Slider doesn't show images

I followed the instructions at:

I created video tutorial for instructions on image slider setup. Please use following link: https://vpthemes.com/how-to-setup-image-slider-on-the-home-page-of-modality-theme/

I created two posts with category “slideshow” and with images. These images show up when you look at the individual posts.

I set up the Theme Image Slider Settings as shown in this screenshot.

When I view the homepage of the site (), I can see the slider alternating between two images, but they are both of the text “Image Placeholder” instead of my images.

Any ideas? Is the size of the images important? Plugins?

Thanks