I did some looking and AU is very much like US in that there are 8 subbands of (8+1) channels. Most gateways, like RAK831, can only deal with 1 subband. In the US, we use the second subband for TTN. I think I said before, that I have to make sure my nodes (and gateway) are set to use this properly. On my RAK wisnode, I have to use a channel mask to mask out the frequencies (channels) that don’t apply, otherwise it will attempt to use them. On some LMIC stacks (and lopy I believe) you have to call enable_channel() and disable_channel() functions during setup() for each individual channel. I have also seen a function called enable_subband() that makes this easier, since it’s only one function call instead of dozens. Perhaps you are in need of doing something like this. It is also my understanding that Australia (and perhaps New Zealand?) also have two other Asian bands in operation making things even more confusing.
When you receive your RAK831, be sure that the global_conf.json file is correct for your region. You will also, likely, need to find the reset script and set the appropriate gpio pin (Broadcom GPIO7) which is pin 11 in wiringPi (python). Apparently the ic880 boards that folks used to use a lot we’re on a different pin (GPIO 17), so you’ll find examples that might lead you astray.
I suggest trying to get everything working with ABP activation as that is one less problem to fight. ABP will work without needing the gateway to send you a confirmation that may or may not be on a frequency your node expects and may or may not be transmitted during the same window of time your node is listening. 