I downloaded the Heywire app to both my iPhone and iPad to see if I could get it to text. This was 30 minutes ago and I have not gotten anywhere with the app. In fact, I get this message (on both devices):
HeyWire is unable to authorize this device. Please check your Internet connection and try again.
I get this message whether I am on WiFi or 4G (on my phone). Nothing works - the app won't even open so that I can sign up for a free phone number.
I say all this because maybe there is something wrong at HeyWire's end. Maybe their servers are down or there is something else wrong. All I can suggest at this time is to set the issue aside and maybe return to it tomorrow. At least, that is what I am going to do...
Have you looked into the app Talkatone? After you get a [free] phone number from Google, you can use Talkatone to send texts with that Google number (you can even make calls). I used it a number of times before I got my iPhone - when I only had the iPad.
Just an idea while you try to resolve this HeyWire issue.