I've been trying to add my phone number and the app won't let me. Twitch support is absolutely awful and you're never going to get a real person, just a copy and paste from the FAQ. First I was told that I was using a VoIP, and I told them I wasn't. They then told me it happens when you've already registered a phone number to an account, and they told me to log into my other account. The issue is I have only ever had one twitch account, and have had this phone number for a coupleish years.