By default, MXT has filters in place to restrict duplicate SMS sending. This was a design feature that was implemented to protect our customers from sending excess messages to the same mobile number and being overcharged.
Importing duplicate contacts is not allowed by default when merging/uploading a contact spreadsheet into MXT contact lists. MXT will automatically remove any duplicate mobile numbers imported into the same contact list.
By default, MXT will also filter out any duplicate phone numbers when sending an SMS through the Upload Send function.
If you wish to allow duplicate contacts to be added to contact lists, this can be completed through the 'Allow Duplicate Mobile Numbers when Importing Contacts into Lists' option within the contact list section.
If you wish to allow duplicates when sending SMS through MXT, such as Upload Send, Campaigns, etc. This can be achieved by disabling the option 'Filter duplicates on send' within your MXT SMS settings.