Unable to select subscription tier level when signing up for Realms Plus

Should I sign up for a Realms Plus subscription through the Play -> "Create your first realm" menu OR through the Marketplace? It's confusing because the interfaces are very different. I read online that I should be able to select an option for 10 players. I also read that I can get my first 30 days free since this is my first time using Realms.

From the main menu, selecting Play -> "Create your first realm" shows a form to create a Realms Server. I can see a Tier section, but the only choice available is "2 Players".

Entering the Marketplace shows an option to purchase a Realms Plus subscription, but doesn't show any option to select which tier I'd like.