Good day and thanks for your mail. The message of "In Muilt-Contact selection mode you must tag at least one Contact." prompt is caused by an INI Setting in your system, which is MS_MULTI_CONTACT. This INI setting allows multiple destination message to be send, once this setting has been turned on, the system will validated and you required to choose at least a contact from the list to be send to.
To bypass this message, you may first select any contact in the list then edit the value in the manual tab. Kindly refer to attached [Step_to_byPass.docx] for more information.