Today we deployed a change to how the Heroku one-click service works. Heroku recently released their European region, and with that change they deprecated the "proxy" subdomain for Heroku apps. To make DNSimple's one-click service compatible with this change, we now require your Heroku app name, as it appears in your herokuapp.com subdomain. When you add Heroku just enter your app name part of the herokuapp.com domain and you should have an ALIAS for your apex domain and a CNAME for "www". You can always add or change these later.
If you plan on using SSL with Heroku then you'll need to change the name that "" and "www" point to to the host name that Heroku provides when you set up your SSL certificate.
Finally make sure to add the custom domain in your Heroku app for both yourdomain.com and www.yourdomain.com. If you have any questions feel free to email us: email@example.com.