You may leave this blank but you must setup your default contacts in the Settings tab. Buttons with blank contact list will use your default contacts.
This is where you can set the contacts linked to your push buttons. The contact phone numbers are where the text messages are sent. The app cannot send text messages without any contact linked to your push button.
To add a contact, tap the '+' blue button at the left top of the screen.
The 'Add a Contact' dialog will display.
In the 'Add a Contact' dialog, enter the contact's phone number in the first text box, and optionally enter the
contact's name/alias in the second text box.
NOTE: The app does not and will not access your contacts in your phone.
Tap the 'Save' button to save the contact and return to the Contacts screen.
The contact you added should now be listed.
To remove a contact, tap on a contact. Then tap Remove on the action sheet at the bottom of the screen.