Indigo airlines ground staff(both Male and Female) is denying to allocate a transit pass of Singapore whereby their own guidelines states below on goindigo.in
"Nationals of China and India can also transit, for up to 96 hours without a visa under the Visa Free Transit facility (VFTF) on either the outbound or return leg of the same journey(but not on both). Leaving the transit area is allowed.
The next flight of the flyer is to China which is a 5-6 hours gap in the next flight from Singapore.