I have a DAC-DEL-TAS route tomorrow on two separate tickets with IndiGo, with a 3 hour layover, both in T3. I was not allowed to check in online for the DAC-DEL leg, but I was able to check in for DEL-TAS and got a mobile boarding pass. The flights are on different passports. Haven't told IndiGo about the T3 transfer. Let's see what happens.