How to Adjust your Player Slots
No server hosted on Proton Cortex has limited player slots, you can adjust this to however many you want. Keep in mind depending on your Plan, you may or may not be able to handle that amount of people.
Stop the server if it's running.
Using the File Manager or SFTP Client, open your server.properties file.
Locate max-players=
Adjust this to your desired value.
Save the file and Start your server.