Out of the schools where the supplemental is simply paying a fee, most of them allow you to just go to their admissions website to find a portal to pay it. No need to wait for an email asking you to do so. If you wait for an email, they will probably send you a "here's what we're still waiting on" email weeks after your AADSAS application is verified. They probably just have predetermined intervals where they auto email everybody who submitted an AADSAS application but still have outstanding materials.
