The registration in GST is PAN-based and State specific. A supplier has to register in each such State or Union territory from where he effects supply if he fulfils any of the following conditions:
1. Having an annual aggregate turnover from all-India operations which is above the threshold limit of Rs. 20 Lakhs (Rs. 10 Lakhs for the North-Eastern States)
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2. Currently registered under any of the earlier indirect tax regimes (VAT, Excise Laws, Service Tax Laws) irrespective of the threshold limit
3. Having branches in multiple states or multiple business verticals in one state
4. Making any supply to other states
5. Required to pay tax under Reverse Charge (In case your supplier is not registered under GST)
6. Required to deduct tax at source or an Input Service Distributor
7. Agents of a supplier
8. Supplying goods or services through E-commerce Operator
9. E-commerce Operator / Aggregator who supplies goods or services under his brand name (e.g. Flipkart, Amazon, Ola)
10. Supplying online information and database access or retrieval services from a place outside India to a person in India, other than a registered taxable person