Why was Iroh put in prison?

because he helped Katara escape with the almost dead 阿凡达 unstead of helping kill her

I guess that he was a refugee that refused to help Azula, so he went to prison instead.

BECAUSE HE BETREYED THE 火, 消防 NATION WHICH WAS KINDA GOOD

Because he became a trader in the eyes of the 火, 消防 nation in the episode where he helped Aang find Appa, and let the half dead Aang escape

he was a wanted traitor the entire time