Am i being thick and missing something? (tech issue)

So, the courier myhermes introduced a new website a month or so ago, since then my work has been able to make new delivery requests.

When you go to pay either via card or PayPal it leads to a page with the header and footter of the website and nothing else, we have tried different computers, different browsers, disabling addons, clearning cache cookies and web data and even tried from a completely different location. There are no blocked popup messages. We can succesfuly use other web stores anywhere else too. A month later of fighting with them in support they still claim everything is working fine and trying to say the issue is on our end without providing any further advice as to what else we can try.

I have a decent amount of web knowledge and considering all of the above, surely the issue has to be on their end right?

Or am I missing something completely obvious?

 

Yep and even in that case it would be on their end as I need to be logged in to go to checkout and click pay, and its logged in after it fails to go to PayPal too