Issue “Not found error"

Hello and Welcome to the forum @AgilexSupport !

There is a known issue about that. It could come from the server version being < 2.11. It could be the case for you as well. Is it possible for you to check the server version (on the UI, you can hover the little heart icon on the bottom right of the screen).
For more info, you can check here as well Passbolt extension chrome - NotFoundError after v4 upgrade (testing, from 2.7.1)