HT Mega Addons Post Slider doesn’t show any image

I installed HT Mega Addons and have been trying to post a Post Slider on my home page. I am currently using the Free Astra theme with the free version of Elementor.

When I use HT Post Grid or HT Post Slider or HT Post Carousel, all the post info looks good, but the image doesn’t appear. Only a large gray box appears.

Can you help me understand why this is happening? I do not have much experience creating web pages with wordpress or with elementor and it is the first time that I use HT Mega Addons. I really want to use this Post Slider since I really like the design it has.

The page I need help with: [log in to see the link]