While generating Live Chat Button code in "Admin Panel->Installation" please make sure to check "Enable Auto Invitation" checkbox shown over the generated HTML code to enable automatic chat invitation, or uncheck to disable.
You may also edit the code directly to disable/enable invitation in the live chat software:
var lhnInviteEnabled = 1; //Enabled
var lhnInviteEnabled = 0; // Disabled
The auto invitation to chat is shown once per hour per visitor, so the same visitor will only be invited once per hour to avoid annoying your visitors with constant invitations to chat.You can always proactively invite visitors to chat by sending a message to browsing visitors.