How to make more training camp?

i see a lot of YouTubers have the ability to level from 50-58 and i only can do from 50-53 what am i missing?

Is your highest character level 54? You can only level with training ground up to the highest level in your roster-1

my main is level 55, how can i level my main fast ?

Boss Rush gives a lot of XP for example, main quest line too. Apart from that just run Legion Raids etc., it’ll come eventually

Edit: you can buy XP potions from Guild vendor or merchant ship in dock (make sure to go there with your main char)

Cube also gives a ton of XP too actually, boss rooms give an on amount but the elite rooms give a fuck ton