I would call. Last year I got no response to emails trying to book a Siem Reap Airways flight REP-BKK. I think Siem Reap (FT) and Bangkok (PG) are same, same, but different.

To take this thread off in a new direction:
If I fly into BKK on PG from Luang Prabang (LPQ), will I have to clear customs and security in order to connect to my TG flight BKK-LAX? Do PG and TG have an interline agreement?