To enable comments you need to be running Ghost version 5.9.0 or higher. For more information, please check the Ghost manual.

The Flux theme supports integrating comments into your Ghost website. This feature is very easy to set up and can be done in a few simple steps.

Step 1: Go to the Ghost Admin, Settings → Membership → Access

Step 2: Click Edit to be able to change the commenting access for your members.

Commenting can be enabled for either All members or Paid-members.

Step 3: Choose your desired option and click Save.