Follow this list to try and fix problems sending messages in Flirt. If the account behaviors in Flirt are automating when you send messages, then your messages are being sent.
Facebook only allows you to send a certain number of messages per day. Check the Message Outbox in the sidebar. You may see that it is still in queue to be sent according to the settings in your preferences. Go to Flirt > Preferences > Account > Behaviors to view how your messages are being automated.
Login to Facebook from a web browser, such as Safari or Firefox and try sending your message. If there is a problem you should see an error. If your account has been suspended Facebook will give you an explanation and walk you through steps to restore your account.
Try sending the message to one of your other accounts to see if it arrives. If the message doesn't arrive your account may be blocked by the recipient.