This involves both versions of SlingPlayer: The standalone application, and the web browser version. Both no longer work with Mac computers.
That's because both versions of SlingPlayer for Mac are 32-bit applications, while Mac computer operating systems starting with macOS Catalina only support 64-bit software applications. Therefore, SlingPlayer software no longer runs on Mac computers if they have been upgraded to macOS Catalina (version 10.15).
Mac computers that have not yet been upgraded to macOS Catalina (version 10.14 and earlier) should continue to run SlingPlayer.
There is currently no workaround for this. SlingPlayer continues to run on Windows computers, iOS devices, Android devices, and Amazon Fire devices.