FleetCapacityExceededException indicates that there are no healthy server processes available on your fleet to host a new game session. In the screenshot posted, Active servers is 0 which corresponds to the same.
- Have you verified that the server starts up correctly? You could potentially test your game server integration with GameLift locally using GameLift local.
- Have you verified your fleet events to check for events that could indicate issues with the server process crashing or terminating in an unexpected manner? You can look for this via the AWS Console or alternatively using the describe-fleet-events command.