AMP is not reflecting

Can you confirm that you have AMP enabled for the specific posts? You can toggle AMP available for individual posts from within your post settings.

That page has a corresponding AMP page:

https://www.veecotech.com.my/top-5-mistakes-your-website-should-avoid-in-2019/?amp

The plugin is working as expected.

Not quite because there is no amphtml link on the canonical page: https://www.veecotech.com.my/top-5-mistakes-your-website-should-avoid-in-2019/

So something is still amiss.

Yep; that means the problem is on the theme side as the link tag is not present. Perhaps it is being removed by a plugin.

We are using AVADA and theme mentioned that it is fully compatible with AMP – https://theme-fusion.com/beginners-guide-integrating-amp-wordpress/

Should i get back to the theme author for this case?

@veecotechweb yes please do.