Inserting into a Page

I’m confused with how to get this to show up on a page in my wordpress blog. I did the following:

1- created a folder and placed my images in it. here’s the path: wp-content/uploads/random404images
2 – created a new page
3 – added the following to that page:

{randomimage}wp-content/uploads/random404images,100%,auto,Random image,https://yittopaws.com/wp-content/uploads/random404images{/randomimage}

4 – then I go to that page: https://yittopaws.com/custom-404-pages/

5 – here’s a screenshot of what I get: https://cl.ly/7a3f6248a6d1

what am I doing wrong?

Thx.
Bruce