Cannot verify server identity

The error suggests that either the website has a misconfigured security certificate - or perhaps something is interfering with the TLS/SSL session between your iPad and the website.

You might start with examining the Certificate details - and if you understand them, the information that you can extract might provide some insight as to why the error/warning is being displayed on your iPad.

A direct check of the Certificate for www[dot]addevent[dot]com suggests that the Site Certificate is actually valid - so the error that you see might imply that a “man-in-the-middle” issue is occurring. Are you accessing this website over a corporate network?

Corporate networks often conduct decryption of secure connections, as part of their DLP and Security mitigations, which will effectively break the chain-of-trust and cause alerts such as yours.

Hello,

You will need to reach out to the website's support for assistance with their product.