Figured it out. Just needed to use an international format for the phone number (put a 1 at the front)

I bought 3 of these buttons. I downloaded the app and got the 1st of them to be seen by the phone. I saved the settings for the location function (entered the number to text and all that). When I hold down the button, the phone makes a ding and then a few seconds later a sort of error noise. No text is ever sent. Do you have an idea what the problem might be?