Note that adding your domain to the PSL has potentially unwanted side effects.

For example, it will become somewhat inconvenient to share data across your subdomains. Instead of just setting a session cookie with domain=.start.page, you will need to implement a proper single sign-on mechanism. Email might be affected, too, especially when it comes to DKIM and DMARC.

You also need to make sure that your domain is listed in the private section of the PSL. There was a thread a while ago when someone got mistakenly listed in the ICANN TLD section and couldn't get a wildcard certificate for their domain. Let's Encrypt and most other CAs have a policy of rejecting domains like *.co.uk, and may rely on the PSL to tell which is which.