 <p>Are you actually typing <code>heroku certs:add PEM KEY</code>? </p> <p>If so you need to replace the words PEM KEY with the filename of your PEM key...</p> <p>e.g.</p> <p><code>heroku certs:add my-site.pem</code></p> <p>The PEM key file is a certificate generated by you or a certificate authority.</p>