Hello archon.  What tournament is it? Usualy if you clear your plarium Play cache, it will solve the problem. If it is the same, maybe you have to contact the Support Team to check it.

That usually happens if the page was unpublished, moved, or had a temporary server issue—try clearing cache/cookies

I'd first check whether the issue is happening only on your end. If other players can access the tournament page without any problems, try clearing the Plarium Play cache and restarting the client. But if the page is missing for everyone, it's most likely an issue on the game's side rather than yours.