This isn't due to, and doesn't impact on, the validity of your license – all licenses purchased before the system was introduced will remain valid as unlimited site lifetime licenses.
Previously most of the plugins didn't require a license key to be entered at all. In the case of Divi Booster there used to be a licensing system in place, but it was removed approximately 5 years ago and since then it too has not required or used license keys.
With the introduction of the new licensing system, it's now necessary to (re)enter the license key to continue receiving updates. Once entered, the plugin should continue to receive updates as normal.
You can find your license key(s) within your Divi Booster account by clicking on "Purchase History" and then the "View Licenses" link next to your purchase.
If you aren't able to locate your keys for any reason, or purchased the plugin from another site (e.g. as part of the Ultimate Divi Bundle), please get in touch and I'll help you get access to your license keys.