Can I add a lap infant to my fare after booking?
 

I want to travel with my son internationally with LATAM in January. I'd like to book the flight now before it gets more expensive, but I don't expect to receive his passport for another 10 days or so. I cannot put him as a lap infant on the reservation without a passport, so should it be possible to book the reservation now, say that I am not bringing an infant, then call them and add and pay the fees on my existing reservation when the passport arrives? Should it be a problem?

Yes, absolutely. I’ve done this for family members a couple of times.

Sometimes the agent doesn’t know the proper procedure. HUACA until someone with experience helps you