If you cannot send a message to a user, please check your credit balance first.
Please be aware that the chat function is enabled only when the user you wish to chat with is online. You may send a mail message while the user is offline, and they will see it once they are back online. If you would still like to send a chat message while the user is offline, please, make sure that you have chatted with this user before. Otherwise, you will not be able to send a chat message while the user is offline.