Heroku: issue with website's security certificate registering custom domain

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http://serverfault.com – I have an Heroku app: https//myapp.herokuapp.com. I want my domain example.com to point to that app, so I: - Registered on Heroku example.com and www.example.com as custom domains - Added the A DNS configuration as on https://devcenter.heroku.com/articles/custom-domains - Added the CNAME configuration www.example.com -> https//myapp.herokuapp.com However, when I type https://www.example.com, the "There is a problem with this website's security certificate" message is displayed on all browsers, before I can enter the site. How can I fix this? Thank you (HowTos)