Mode C Not Working / Working Again

6 turns, word for word from the oral. Read the pilot lines out loud.

The exchange

6 turns in order

You, the pilot

Delhi Control IFLY 160, unable RVSM due equipment, position 50 DME JJP, passing FL 260, request maintain FL 280

ATC

IFLY 160 maintain FL 280, on reaching

You, the pilot

Will maintain FL 280, on reaching IFLY 160

You, the pilot

Delhi Control IFLY 160, ready to resume RVSM, maintaining FL 280, request FL 320

ATC

FL 320 not cleared, maintain FL 280

You, the pilot

Maintaining FL 280 IFLY 160