Does a license work for unlimited pages
No. As with all common software/SaaS licenses, this license key is for 1 ManyChat account/Facebook page.
However, you CAN use the license for another page for each App. For example: if you use dynamic images on page A, and a webview form on Page B, then that is possible.
The First time you use the license key on a page, the unique match “key <> page” is created. You can use the Free token in the App settings to test it on any page, once you decide to use it on the page “for real”, just change the Free token to your license key.