Fix: The start address is not valid for this content source type
Ever get this error when trying to add a content source in SharePoint Search?
This is because of the option “Crawl everything under the host name of each start address” which will accept only the host names(like https://sharePoint.com) and not the Sub-site URLs(like https://sharePoint.com/sites/abc/default.aspx)
If you enter https://sharePoint.com/sub-site/default.aspx and select “Crawl only the SharePoint site of each start address” then SharePoint will crawl from the top-level site of the given URL entered. Here SharePoint will crawl from https://sharePoint.com/ and all its sub-sites.