Can't lvl up past lvl 284 and 7 stars

It seems I cant lvl past lvl 284 and 7 stars and I’m wondering why since I encountered lvl 290 in the Arena…
Is there someone who knows why?
Thanks a lot.

Both are from getting high enough in Advance Powerups (Legendary Runes)

If you get “Increase heroes’ evolution cap: 2” I think that’s when you get 8 stars.

“Increase heroes’ level cap: 10” will get you to 290

You must keep collecting more Legendary Runes (the yellow ones) to unlock these power-ups. For faster progress I recommend to buy them from the arena shop whenever they appear there, or else it’s gonna take very-very long time looting them from the daily Dark Rush challenges on Tuesdays and Fridays. The reward amount of Runes there seems to be decreased since the last bigger update (always under 50 only), so now it’s much harder than before to earn them, though the newest power-up upgrades are very expensive, 500 Runes per level and the 8-star evolving is still not available yet…