To claim the business trip credit, you simply have to select the "This is a business trip" option when booking, this worked for me. Please comment if this is no longer the case.
Got an email about the updated referral rate, also been keeping an eye out for our upcoming trip.
Thought it'd be a good way to introduce everyone who wasn't aware to the referral system.
At the bottom of this post there will be a grey box with either my username and random, or just random.
Choose either of those to be taken to the Airbnb referral sign up page and to receive your credit. To add your own referral link, click 'Edit' on the right side of the same box and follow the instructions.