When you said you got the correct availability and fare classes, where did you get it from?

Did you know what the PXXX was combinable with, or just assumed it would work for the airlines you want?

I can see airlines not being particularly excited/in a hurry to sell you a J ticket to BKK for $2800, but you did end up getting a call back and a quote at the price you wanted.

Usually, if you get ITA matrix to quote it, and there's no weird availability issues it's not picking up (where AC inventory available is different), giving the booking codes and flight numbers should work. I think it worked for every FTer trying to do what you're doing.