This discount requirement can be only used with a discount where the Discount type is set to Assigned to order subtotal as displayed in the image below.

discount cart subtotal configure

 

The discount requirement can be only configured if the discount type is properly set as mentioned above and the discount is saved.

To understand usage of this discount requirement please see the image below.

discount cart subtotal requirement

As explained above, Minimum cart subtotal should be x.xx amount should be selected as Discount requirement type and the Required cart subtotal value must be also provided. Once saved, the discount requirement will be added to the discount as displayed in the image below.

discount cart subtotal requirement group

That's all you need to do in order to use this discount requirement in your nopCommerce store.