Dear Sir,

Please confirm my understanding. You flew from CEI(Chiang Rai) to BKK, aren’t you? That is a domestic flight. C1 is an international gate. In Suvarnabhumi airport, they use gate A and B for domestic flights. In your case, PG may have used the aircraft for an international purpose afterward. If any ground staff allowed you to use that gate, it would be illegal in Thailand. You would be in an international area without passport stamp and X Ray. If your passport is already stamped from CEI, you have to pass a X Ray check point in Suvarnabhumi.