Step 1.
Click Messaging from the main menu, then click on Mobile Campaigns.

Step 2.
Click the pencil icon in the edit column next to the Mobile Campaign you wish to restrict users from opting into multiple times.

Step 3.
Click the Opt-In Management tab and click the radio button to turn Opt-In Management “ON”

Step 4.
Leaving “Contest (Restrict Opt-ins)” selected, use the # Of Opt-Ins Allowed and (X) Days drop down menus to set your restrictions.

Step 5.
Type the alternate message users will receive once they've reached their opt-in limit. 

Step 6.
Click the UPDATE button to save your changes.