Since people can't read existing forum posts, the FAQ, or the Supported Device list...
That model is NOT supported. It never was, and it's even less supported since Asus is now enforcing stricter model validation on the RT-AC68U series at flash time. It doesn't matter whether you converted it, hacked it, repainted it, or whatever. Stop asking on the forums for help flashing your RT-AC68U when you actually have a TM-AC1900 - it's NOT supported, period.
That model is NOT supported. It never was, and it's even less supported since Asus is now enforcing stricter model validation on the RT-AC68U series at flash time. It doesn't matter whether you converted it, hacked it, repainted it, or whatever. Stop asking on the forums for help flashing your RT-AC68U when you actually have a TM-AC1900 - it's NOT supported, period.