Unable to check out or view shopping cart on my iPad on a website

Your description suggests that your iPad may be blocking some cookies or other elements associated with this particular website - very often this being the initial cookie-acceptance page being blocked prior to acceptance.

Are you using a Content or Ad-blocking service or App?

As a diagnostic exercise, temporarily disable Safari's Content blocker:

Refresh the webpage; if you see a cookie acceptance prompt, respond as appropriate - then use the website as normal. Does this resolve or change the apparent behaviour difficulty?