When a visitor uses our chat, there is no "start button". The visitor doesn't have to fill in any contact details or activate the chat to make it start – the chat widget is just there on your website, and the only thing the visitor has to do is to type a message when you're available and Online in the chat.

For the same reason, a certain kind of technique is required to determine if you're free to chat or not, and this is where we use slots. Your number of slots means the maximum amount of chats that you can have open, or receive, at the same time, which you set in Settings > Messages > Max active chats. 

When you have many visitors on your website, or you have many visitors who want to start a chat with you at the same time, it might happen that the widget can't read how many free slots there are.

Let's say for instance that two or more visitors have typed their first message at the same time, but neither have sent their messages. As long as the messages haven't been sent, there are still free slots and the input field is still available for visitors to use. The slots also need to be avaliable as we don't know who will actually start a chat and send a message. 

To sum this up, the slots are available and free when the visitors start typing their messages, but when the messages are sent, the slots can't always decide which visitor to let in. The visitors have semi reserved the same slot, so instead of letting only one visitor in, the slot lets both of the visitors in.