I have 4 accounts (3 are team Valor) level 25, two level 30's, and a level 31 team Mystic. Most of the gyms in our city tend to be Valor yet I can rarely join (when there is room for many more Pokemon and has lots of prestige points). I can train there forever but it never let's me join. No I don't already have a Pokemon in a gym, yes I know how to join a gym, yes I know how to identify if it's the correct affiliated gym. Are there some requirements I am not aware of? Because I have at one time joined a gym with all 4 of my accounts. The only thing I haven't done in a while is take down any gyms, I just train in my team gyms. And when I can join (but don't) it doesn't always give the options for my other 2 accounts to join, it's just random. Thanks in advance.
Before I answer, a few things. According to Niantic, you are not allowed more than one account.
Don’t do it. Play fair. Pokémon GO is meant to be played on a mobile device and get you outside to explore your world! Methods of cheating, unfortunately, are limited only by cheaters’ imaginations, but include at a minimum the following: using modified or unofficial software; playing with multiple accounts (one account per player, please); sharing accounts; using tools or techniques to alter or falsify your location; or selling/trading accounts.
Read it from the source https://support.pokemongo.nianticlabs.com/hc/en-us/articles/221993967
It also looks like you are GPS Spoofing. This is also illegal in Pokémon GO.
As for the actual question, you may have been soft banned. This is for not abiding by their rules. There is a solution for this: spin a Pokéstop repeatedly until you regain access.
There may be a "Network Error"
Spamming the "Add a Pokémon" button also caused you to put a Pokémon in a gym without you knowing
Finally, the only requirements are:
- A suitable distance away from the gym
- The same team
- No SoftBan on at the moment
- Enough Prestige
- Amount of time for the battler to place in the neutral gym If you have made sure if all of this, then there is no method of fixing it. You should look on Reddit - people rant about this all the time