I don't think these are what are causing the issue here, but two things I noticed from the video
1. At 29:46 in the video you paste the Device EUI into the Quickstart sketch instead of the App EUI. But at 34:05 with TheThingsNode basic sketch you appear to paste the correct values.
2. At
https://www.thethingsnetwork.org/country/australia/ you will see a note that you can't legally use the units bought from USA in Australia. The USA units could use channels outside the ACMA ISM allocation*, i.e. in tha 902-915MHz range used by GSM here (being phased out, and reallocated). That page also states for Australia: "We use Frequency Sub Band 2, also known as channels 8-15, or 916.8MHz through to 918.2MHz".
That said, the fact you selected the AU frequency plan when adding the gateway should configure the gatway to make use of the correct config file (i.e.
https://github.com/TheThingsNetwork/gateway-conf/blob/master/AU-global_conf.json) and thus use the correct 8 channels for Australia. I just think the models sold in Australia have to have the extra frequencies locked out in the radio module firmware.
There generally seems to be a lot of confusion about supporting AU915 band. I have to guess that this is why my TTN gateways & Uno I ordered back in 2016 still haven't shipped, although they say they passed RCM testing so they must have something...
e.g. see
https://github.com/TheThingsNetwork/arduino-device-lib/issues/222 which is still open
Back to your issue, the messages you're getting near the end certainly seem to indicate there is communication between node and gateway and TTN backend, but the authentication of your App EUI & key are failing. Not having yet had a chance to work with TTN, I don't know where things are goign wrong. I think I'm going to order a RAK831 based gateway to get up and running as I've got a bunch of nodes sitting here that I can't really try out without heading to another site in Sydney.
There is a similar report of "join not accepted" on the forums with some potential fixes (create a new App, reset the frame counter in the console)
https://www.thethingsnetwork.org/forum/t/join-not-accepted-denied-rn2903-rf-click2/9570/3Otherwise, I wonder if you can get debug messages out of the gateway to see what is happening?