Works even on award ticket
I had even taken my 1 year old from ATL - BOM (via AMS) on an award ticket 4 years ago in J as a lap infant. My wife and I had sky peso award tickets and I just had to paid 10% of the cheapest business fare that was available then for my 1 year old (came to about $600). So you definitely do not need to pay a full fare ticket for your infant! Whoever you talked to at DL has zero clue.