A. Section 22 (1) states that 'every supplier shall be liable to be registered under this Act in the State or Union territory, other than special category States, from where he makes a taxable supply of goods or services or both, if his aggregate turnover in a financial year exceeds specified limits.
A1. As per Section 2(108), Taxable supplies include “taxable supply” means a supply of goods or services or both which is leviable to tax under this Act. And as per Section 2(6), “aggregate turnover" include taxable as well as exempt supplies.
B. Section 23(1)(a) states that 'any person engaged exclusively in the business of supplying goods or services or both that are not liable to tax or wholly exempt from tax shall not be liable to registration'
C. Section 25(1) states that 'Every person who is liable to be registered under section 22 or section 24 shall apply for registration in every such State or Union territory in which he is so liable within thirty days from the date on which he becomes liable to registration, in such manner and subject to such conditions as may be prescribed'.
D. Section 25(4) states that '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 this Act.'.
E. Section 25(5) states that 'where a person who has obtained or is required to obtain registration in a State or Union territory in respect of an establishment, has an establishment in another State or Union territory, thensuch establishments shall be treated as establishments of distinct persons for the purposes of this Act.
Collective reading of above provisions, in my humble view, means the following in the context of query raised here:
1. "Mandatory" registration u/s 22(1) is state / UT specific.
2. Merely because a tax-payer has obtained or required to obtain registration in one state u/s 22, he need NOT take registration for other business establishments which is lying in other states / UT IF these other business establishment/s are engaged exclusively in the business of supplying goods or services or both that are not liable to tax or wholly exempt from tax AND IF these other business establishment/s are NOT required to take registration u/s 24.
3. For purpose of GST Act (including Section 20), 'business establishment which is registered in a one particular state' and 'other business establishments which is lying in other states / UT' are treated as 'distinct person'even when these other business establishment/s are NEITHER registered NOR required to be registered under GST.
4. For purpose of GST, 'business establishment in Andhra Pradesh' (as per facts given in the query) is 'distinct person' from 'business establishment which is registered in Karnataka' and such business establishment in Andhra Pradesh is exempted from taking registration under GST u/s 23(1)(a),
5. Above position of law becomes more apparent if one notes "difference" between sub-section (4) & (5) of Section 25 and law-maker's need to make these separate provisions.
These are ex facie views of mine and the same should not be construed as professional advice / suggestion.