How to purchase a license that meets Edge sync pre-requisite.

First you would need to have an account under Azure Portal. If you don't have one, create a new and this would be your Microsoft account.

Sign-in to Azure portal using the same account. You can see the account type under Azure Active Directory. For you to own a license you need to have a "Global administrator" account. Which means you need to create a new user.

How to create a new user under Azure active directory and set the role.

How to purchase license using global administrator account

Next step would be, to learn how to enable AIP.