Its not invite only. Just the eligibility criteria is not exactly public. RM and BM are useless. Most of them don't know much apart from selling policies.I am trying to get Infinia for a long time, spoke to even the RM & BM, but its invite only.
What is your current credit limit on DCB?
The current upgrade criteria for Infinia is 9L+ spends in 6 months and 8L+ credit limit. If you satisfy both, upgrade through PNO is possible.