In order to enable Magento 2 Dynamic Categories Extension navigate to Stores > Configuration > Magefan Extensions > Dynamic Category.
General Configuration
1. Enable the extension in order to be able to create dynamic categories.
2. Enter the Product Key which you can find in your Magefan Account > My Downloads.
3. Enable the Use MSI option if you want to use the Multi-Source Inventory on your store.
Once you've finished don't forget to press the Save Config button.