I did not know where to report this, rather silly, thing.
This documentation:
https://www.revenuecat.com/docs/tools/customer-center/customer-center-flutter
States that we need at least version 8.7.0

Well, the latest release of that package in pub.dev in 8.6.1 at the time of writing and the changelog:
https://pub.dev/packages/purchases_ui_flutter/changelog
says you introduced the customer center at 8.6.0
Great product guys, thanks!!