This has happened to me before. Their excuse is that they need to "write something" on the transaction so it appears on your bank statement.

I've had them ask the question two different ways "what's it for?" and "how do you want it to appear on your statement?" which makes me suspicious they've been trained to say it a particular way but sometimes revert to the real reason.

I usually just say "renovations" or something similar regardless of the real reason and go on with my day.

I know for a fact that some banks in Australia don't like crypto. There's plenty of stories of people having transactions blocked to crypto exchanges. Some banks block all of them.

I also know for a fact they monitor your transactions, even small ones. A couple of years ago I transferred some small amount of money (like $100) to Binance and about 20 mins later someone from the bank called me and said my transaction had been "flagged" as suspicious. I explained to her I knew what I was doing and it was only a small amount and she let it through and told me it won't happen again.

Earlier this year, payments in and out of Binance were mostly blocked in Australia via the 3rd party payment provider under the excuse of "protection against scams". I wasn't using Binance anymore when this happened.

I should also mention that I have tried to find Bitcoin only exchanges in Australia but the very few that exist are terrible. Currently I use Kraken but I only buy Bitcoin and I withdraw regularly. So far, my bank hasn't blocked me but the fiat deposits can take multiple days.

Kraken support reached out to me one day and told me I should make my deposits more "random" amounts like $99 or $101 to throw off the tracking. Again, pretty messed up that we need to be doing shit like that.