Hello student, 

NRI quota are seats reserved for non-resedential Indians and are not available for Indian nationals. The number of seats available may vary from institute to institute, and there is no fixed number of students that they may admit. In fact, some institutes create supernumerary seats for NRI students, above and over the regular seats.

As for the mode of payment, it has to be done in online mode. The full details can be found on the institute website.

Cheers!