@MKAY hey, thanks for your question and welcome to the community!
Before we go any deeper into this, do you perhaps have access to multiple Klaviyo accounts? Being logged into one Klaviyo account while trying to click on a link for a piece of content from another account typically throws this exact error.
Other than that, it might really be a glitch which unfortunately does require the support team to resolve this ticket for you.
Have you tried using other browsers/devices to log in and access this? It could be a cache issue as well, potentially.