PHP contact form

I made my first succesful heroku app.
https://php-contact-form-002.herokuapp.com/

For some reason, it doesn’t seem to be sending the email.
When I did this on my own localhost server, it sent it, but when I sent it off of heroku, it never sent the email.

If you know why this is happening, please tell me.
Here is the github repo: https://github.com/Conner1115/Contact-Form

All feedback will be appreciated (Bring on the critisiscms!)
Thanks.