Why doesn’t “Tap Notify” work on my iPad?

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Just found the app Tap Notify. It could be the perfect solution for my son with a disability, just what I’ve been looking for. I installed it on his new iPad. I tried sending a message to my phone from his device but I get “Message Failed to Send” on his device. I tried sending it as an email. Same “failed to send” message. I tried restarting the iPad. Still didn’t work. I installed the app on my very old iPad. I get a “Message Send Error” that says “Unable to send message”. I got this message after restarting the iPad. Please help.

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