G'day Graham,
I found this link and am also copying the specific reference that I found. I hope it helps, but if not, please feel free to post again and I will retry to help.
www.pmi.org/certifications/certification...1b-bca4-c6612c424c05
The above link had the particular excerpt below, but I had to scroll down to the bottom to find it.
How do I schedule for an online proctored exam?
Before you can schedule your exam you must submit your application payment. Once payment is received, you will then be eligible to schedule your online proctored exam. Log in to PMI.org and navigate to “Review Application Status” under myPMI. Click "Schedule Exam". You will be directed to schedule your online proctored exam through Pearson VUE.