GST is the product of the biggest tax reform in India which has tremendously improved ease of doing business and increasing the taxpayer base in India by including millions of small businesses. Tax complexities would be reduced due to the abolishing and subsuming of multiple taxes into a single, simple system.
The new GST regime mandates that all entities involved in buying or selling goods or providing services or both are required to register and obtain GSTIN. Registration is mandatory once the entity crosses a minimum threshold turnover or when an individual starts a new business that is expected to cross the prescribed turnover
If you are engaged in the supply of goods or services to customers in another state then regardless of turnover, you need to obtain the registration before commencing any interstate trade.
If the aggregate turnover is more than 20 lakh (Rs. 10 lakh for North Eastern States) then GST registration is necessary and must be obtained within 30 days of reaching to that level.
It is compulsory irrespective of the turnover, for casual taxable person, or those need to pay tax on RCM, Non-Resident taxable person, Input Service Distributor, E-commerce Operator, etc.
A person who was registered under any previous law of indirect tax was required to migrate to GST, however if failed then immediately get yourself registered under GST.