The broadcast service has had its troubles.
A few people mentioned that the trick mentioned here worked for them:
https://answers.microsoft.com/en-us/office/forum/office_2010-powerpoint/error-starting-broadcast-with-powerpoint-2010-but/91b76df3-6a1c-4ca6-95f0-bc2030383566
That's pretty old, though. This is more recent and suggests that the service behind PPT broadcasting is dead:
https://support.office.com/en-US/Article/Discontinued-features-and-modified-functionality-in-Microsoft-SharePoint-2013-bbbb0815-2538-4f1d-b647-1f7f6d508c93#__toc382936211
Note that the broadcast service is not the same as PowerPoint Online, which is a free PowerPoint viewer and lightweight editor for PowerPoint files. The broadcast service integrated with the viewer (an older version of it, I believe) that allowed you to control the flow of a show that your audience watched in the viewer.
Without the broadcast component or software installed, at least temporarily, on the audience PC, you may not be able to control what they see. You might need to resort to having them watch using the online version and direct them to advance slides over a phone line. Shades of "Next slide, please."