GST: In what form can a return be submitted by a non-resident person?

The writer is tax partner, PwC India

A retired architect/engineer rendering services only in state A. His fees are substantially below the exemption limit of Rs 20 lakh. He has rendered negligible services to one or two clients in state B, for which he has charged small fees. Whether he will be liable for compulsory registration? If yes, is he entitled to claim an exemption in state A, which is substantially below the exemption limit? Is there any remedy for such service provider to retain his exemption when in one or two cases small fees are received from another state?

If the location from where the services are