Almost certainly a failure on our end, which almost certainly makes it my fault. Sorry about that! Your membership has now been added, with a little extra for the trouble.
Seems that some code changes I made to the payment handler resulted in nothing happening after PayPal notified our system about the payment. Which is weird, given that it worked when I tested it with my own credit card! I've put the old code back, so future payments should be OK.
There's a small possibility that my code is fine and PayPal simply didn't bother telling our systems yet, but the timing suggests that this is my fault.
We didn't get an email notification from PayPal either, we must look into that.
Once again, sorry for the mess.
My friend and I applied for airline jobs in Australia, but they didn't Qantas.