Who can open the app
Settings > App access names the app admins. Add a person or a SharePoint group. The list holds 40 entries. Site owners can always open the app and change settings. Search still respects SharePoint permissions. An app admin sees only the content that account can already open.
Subscription
One yearly subscription is $499 for unlimited users in the tenant. A 14-day trial starts on first use of the site. During the trial the app shows a notice with the days remaining and Subscribe. Close that notice with the dismiss control. It stays closed for that trial end date.
Subscribe opens checkout. Open the billing portal manages an active subscription. Checkout and the portal run on the Chronodat subscription service for the product searchhub-365.
When the trial has ended and there is no subscription or valid key, work pages show the paywall. Subscription still opens, so someone can subscribe or paste a key. If the subscription service cannot be reached, the app says so. It does not treat a network problem as an ended trial.
License key
A signed license key is another way to open the app. A site key must match this site. A tenant key must match this tenant. The key is checked in the browser.