In version 2 of YouTube's API, it was possible to get a RSS feed containing only a single, specific video.
However, when YouTube shut off V2 of the YouTube API and moved to the V3 API, channels and playlists got new Feed URLs, but single videos did not get a new feed URL to replace the old one. (This is a YouTube feature, not a RSS Authority Sniper feature)
So when RSS Authority Sniper looks for a single post feed, it can't find one because it no longer exists.
The Work Around:
Here is one way to manually generate a feed for a single video so that you can use it inside the application.
1. Create a playlist on your channel that contains only the single video.
2. Then get the playlist RSS feed and put the playlist feed in the single post feed box.
Once you have entered a valid feed into the single post feed box, the application will accept it and run as normal through the rest of the process.