Once you've passed the Install Check, you will be prompted to choose a subscription before the site goes active.
Note: Every time a new device is added and saved, the subscription pricing will get updated accordingly depending on the total number of devices attached on the site.
Where can I get the tax receipt for the chosen subscription?
The tax receipt will be sent to the email of the user commissioning the site. As highlighted in the screenshot above, the user can change the email address to their 'accounts' or 'admin' email so that they receive the email instead of the user commissioning the site.