Supply by a Taxable Person Under GST
A supply to attract GST should be made by a taxable person. Hence a supply between two non-taxable persons does not constitute supply under GST. A “taxable person” is a person who is registered or liable to be registered under section 22 or section 24. Hence even an unregistered person who is liable to be registered is a taxable person. Similarly, a person not liable to be registered but has taken voluntary registration and got himself registered is also a taxable person.
It should be noted that GST in India is state-centric. Hence a person making supplies from different states need to take separate registration in each state. Further the person may take more than one registration within a state if the person has multiple business verticals. A person who has obtained or is required to obtain more than one registration, whether in one State or Union territory or more than one State or Union territory shall, in respect of each such registration, be treated as distinct persons for the purposes of GST. Hence a supply between these entities constitutes supply under GST.
Source: CBIC Website