Sendgrid links in email produce Your connection is not private error in browser

Have you enabled SSL Click Tracking on your SendGrid account?

That error is generally because you're moving from an HTTPS > HTTP connection, or vice versa. If you have SendGrid's Click Tracking enabled, but don't have SSL enabled, their tracked links will be http://, even though your base link is https://.

I have found the problem.

I did not use the correct URL for my app on Heroku.

config.action_mailer.default_url_options = { host: 'https://provenword.herokuapp.com' }

I had written heroku.com instead of herokuapp.com

Thanks to everyone for their assistance.