My AMP html is valid but not appearing as AMP in facebook post or google search results

This is my Non AMP site with amphtml link available, As we know that Facebook is currently showing amp pages if it's availble, But when I posted the above url it doesn't link it to my amp page.

I also tried g.co/ampdemo/ it doesn't show the amp version. Am I missing anything here ?

Note: Page passes amp validation.

Solution

So the problem was : AMP error: Missing supported structured data element

It is no where mentioned that you also should have to add structured data element in the AMP html page.

But If you don't have Structured data element Google or Facebook invalidates the amp html page.

But so is no the case with AMP Validators my page passed all amp validators.