Bolt

Agoda.com - Platinum (highest level, only requires 10 bookings in 2 years)
Booking.com - Genius level 3 (highest level, only requires 15 bookings in 2 years, and you attain it for life)
Trip.com - Gold (highest level is platinum)

Referrals
CashRewards - https://refer.cashrewards.com.au/x/oXGMjY - You get $20, I get $40. As far as I know, $20 is still the maximum signup bonus, and is what I got when I signed up. It's a good site to use for both online and in-store shopping to get extra free cashback. It's a must for any bargain hunter's tool belt. Even sites where you already get bargains like eBay, and Amazon. The way it works is for online stores, you either use the browser extension, or click through from cashrewards to make your purchase. For instore payments, you register your credit card number, then just pay as normal.

UBank - 18X6THM - We both get $30 if you open a free spend account and make 3 card purchases. I think it's good because UBank has consistently had the best savings interest rate for over a decade, so you can keep your transaction account close to your savings account for maximum interest. I think it's good to use as an account to have an automatic credit card payment come out of so that you get an extra 44-55 days interest free depending on the bank. The spending account is also pretty good, as it's feature rich, and free. It's good for international use if your credit card provider doesn't offer fee free international transacitons, and it supports all of the digital pay providers including Apple Pay and Google Pay. Go here for more details. https://www.ubank.com.au/refer-a-friend