I bought a cheap SSL (RapidSSL), with CA too. It’s not self-signed.
Then I want to use it with my facebook application.
If I open my page outside the facebook, it says everything is okay with my SSL, but if I want to open my app in secure browsing, FB shows blank page 🙁
https://specialpromotion.hu/fb_kviz/
here you can see, that the SSL is working fine.
https://apps.facebook.com/estikviz/ and it works fine too, with this link. But my fb page shows blank only 🙁
You need to set the HTTPS URL as the Secure Canvas URL, and the non-HTTPS URL as the Canvas URL field in the App settings
Note, you need to provide both; not just a HTTPS URL in both fields, or HTTPS only in the “Canvas URL” and nothing in the “Secure Canvas URL” field