Playback is a chain
The browser first resolves a host, negotiates HTTPS, requests a manifest, chooses a variant and then requests media segments. A successful response at one step says nothing about the next. Good diagnostics record the first failed stage instead of reducing every problem to ‘offline.’
Web-specific restrictions
Browsers enforce cross-origin and mixed-content rules that many desktop players do not. The manifest and every derived segment must be HTTPS on an HTTPS page, and relevant responses must permit the website origin. Redirects can introduce a failure even when the first URL looks correct.
What viewers can try
Confirm that the channel is allowed in your region, try a current browser, disable aggressive network filtering for a moment and read the precise status message. Do not paste private signed addresses into public diagnostic services. If the stream belongs to you, inspect the browser network log and fix the earliest failing request.