Why can I leave my Pokémon at some gyms but not others?

[AC Question]

I have noticed that I cannot leave my Pokémon at some gyms even though they are my team color.

 

[fuzzylumpkin]

The gym can only hold an amount of Pokémon equal to its level, So a level 4 gym can hold 4 Pokémon. To increase the gyms level you have to battle it to increase its prestige.

Posted via the Android Central App

 

[iphoneh8r]

It's all based on prestige. Lower gyms prestige to knock other teams gyms off of it, raise your own team gyms prestige to add Pokemon.

 

[erwaso]

You need to fight them one on one before it allows you to leave one if your own