Argo Tiered Caching

I have other sites in my account that allow Argo Tiered caching.
But one of my site is not allowing it.

But the above site is throwing error.
BTW, is the above feature free or paid.

Please resolve the issue

Site loads everywhere I checked, such as on GTMetrix.

I am talking about Argo tiered caching. I’m unable to enable it.