Hello, Magento Buddies!!
When the total of a bill reaches zero, it is considered a zero subtotal checkout. The discount must be applied here in order for the discount to be applied. Zero subtotal checkout must be provided by the admin. Have a look at How to Configure Zero Subtotal Checkout in Magento 2.
Complete Guide by How to Configure Zero Subtotal Checkout in Magento 2
submitted by /u/themagecomp
[link] [comments]