LocalHost: 8000, 404 Error page not found

Hello I am work on the Introduction to data frames for R coding.
However, the locahost keeps having a 404 error.
I have tried Chrome and Firefox, cleared my cache, made sure both browsers & all extensions are up to date. Also, set Ad Blocker to never run for this site.
Unfortunately, still nothing.
If anyone has a solution please let me know.

The R Lesson URL: