We’ve temporarily disabled the ability to send Berries to Pokémon defending Gyms through the Pokémon info screen to resolve an issue.

Trainers incorrectly receive "The Gym is under attack!” error message

Resolved
Last Updated: 07/19/2017

Some Trainers may experience a bug where they are unable to assign a Pokémon to a Gym shortly after the Gym was claimed for their team. Attempting to assign a Pokémon returns the error message: “The Gym is under attack! Try again later.”

Update:

One of the root causes of this issue has been resolved in Pokémon GO version 0.67.2 (1.37.2). We’re actively working on a fix to completely resolve this issue.

Update 2:

We believe this issue is fully resolved in Pokémon GO version 0.69.0.