A private browsing window (also called Incognito Mode in Chrome, Private Window in Firefox and Safari, or InPrivate in Edge) is a browser mode that prevents your browsing history, cookies, and site data from being saved after you close the window.
The issue with trying to use a private browsing window when accessing your live stream is that it will not store the session and therefore will block you from accessing the stream.
To watch the live stream you have purchased please first make sure that you're not using a private browsing window or private browser (eg. duckduckgo).
If you're unsure if you're in private browsing window, look for an indication like a darker browser theme or a special Incognito/Private Browsing icon (usually a hat and glasses or a mask).