What are the cases in which registration is compulsory

As per Section 24 of the GST Act, the following categories of persons shall be required to be registered compulsorily irrespective of the threshold limit:
(a) persons making any inter-State taxable supply;
(b) casual taxable persons making taxable supply;
(c) persons who are required to pay tax under reverse charge;
(d) non-resident taxable persons making taxable supply;
(e) an electronic commerce operator for whom the provision of section 9(5) of GST Act apply.
(f) persons who are required to deduct tax under section 51;
(g) Every electronic commerce operator;
(h) persons who supply goods or services or both on behalf of other taxable persons whether as an agent or otherwise;
(i) input service distributor;
(j) persons who supply goods or services or both, other than supplies specified
under sub-section (5) of section 9, through such electronic commerce operator who is required to collect tax at source under section 52;
(k) every person supplying online information and database access or retrieval
services from a place outside India to a person in India, other than a registered person;
(l) such other person or class of persons as may be notified by the Government on the recommendations of the Council.

(ICAI FAQ PUBLICATIONS 06-09-2017 REGISTRATION: FAQ NO. 17)

What is aggregate turnover

As per section 2 (6) of the GST Law, aggregate turnover means the aggregate value of all taxable supplies, exempt supplies, export of goods or services or both and inter State supplies of persons having the same PAN, to be computed on all India basis and excludes CGST/SGST, IGST, UTGST and cess. Aggregate turnover does not include value of inward supplies on which tax is payable on reverse charge basis.

(ICAI FAQ PUBLICATIONS 06-09-2017 REGISTRATION: FAQ NO. 17)

Who are the persons liable to take a Registration under the GST Law

Every supplier whose aggregate turnover exceeds Rs. 20 Lacs (10 Lacs for special category states) in a financial year is liable to get himself registered in a State from where he makes taxable supplies. However, certain categories of persons mentioned in Section 24 of GST Law are liable to be registered irrespective of this threshold. Further, following persons shall not be liable to register as per section 23: –
(a) An agriculturist, to the extent of supply of produce out of cultivation of land.
(b) Any person engaged exclusively in the business of supplying goods and/ services that are not liable to tax or wholly exempt from tax under the CGST Act or under IGST Act.

(ICAI FAQ PUBLICATIONS 06-09-2017 REGISTRATION: FAQ NO. 16)

What will be the effective date of registration

Where the application for registration has been submitted within thirty days from the date on which the person becomes liable to registration, the effective date of registration shall be date on which he become liable for registration. Where an application for registration has been submitted by the applicant after thirty days from the date of his becoming liable to registration, the effective date of registration shall be the date of grant of registration.
In case of suo moto registration, i.e. registration pursuant to any survey, enquiry, inspection, search or any other proceedings, the effective date of registration shall be the date of order of registration.

(ICAI FAQ PUBLICATIONS 06-09-2017 REGISTRATION: FAQ NO. 14)

Is it necessary for the foreign embassy’s to get registration under GST Law

All UN bodies, Consulate or Embassy of foreign countries and any other class of persons, so notified, would be required to obtain a unique identification number (UIN) from the GST portal. This UIN will be needed for claiming refund of taxes paid by them on the notified supply of goods or services or both received by them.

(ICAI FAQ PUBLICATIONS 06-09-2017 REGISTRATION: FAQ NO. 11)

Whether the Department through the proper officer, can suo-moto proceed with registration of a Person under the Act

Yes. In terms of sub-section (8) of Section 25, where a person who is liable to be registered under the CGST Act fails to obtain registration, the proper officer may, without prejudice to any action which may be taken under the CGST Act, or under any other law for the time being in force, proceed to register such person in the manner as may be prescribed.

(ICAI FAQ PUBLICATIONS 06-09-2017 REGISTRATION: FAQ NO. 8)