Are you able to read any preview chapter on the J-Novel site?
There are known issues with Nord VPN and the J-Novel site.
If you use Nord VPN, don't at J-Novel.
Just confirmed that I'm able to read the first section of...wait.
You say you purchased Volume 5, yet your screen shot is of Volume 3?
Maybe you want to make sure you are opening the proper volume.
In any case, what you'll read on the web site is the pre-publication version, which will have errors that won't appear in the finished volume; better to download and read using an ebook reader since you've purchased the final edit version.