How it is possible to add a alert to inform the customer regarding critical situation. E.g. The license will expire soon.
I have opened up a feature request (https://jira.atlassian.com/browse/BSERV-10323) to make this public which you can vote on and watch for updates, but we can’t guarantee its priority or completion date.
Until then, the accepted way for plugins to provide these kind of alerts is by placing an
aui.message.error banner (see https://docs.atlassian.com/aui/6.0.9/docs/messages.html for details) in the web panel
bitbucket.notification.banner.header (see https://developer.atlassian.com/bitbucket/server/docs/latest/reference/web-fragments.html for details)
This will look something like: