This has plagued me for years. Your home network is set up exactly as it should be, and folders shared as per instructions. You get prompted for network credentials, and nothing you enter in the box works. Infuriating. Nine times out of ten it’s quicker to transfer the files with a pen drive.
I finally found a solution and these people should be given a Nobel prize. Follow this link: Enter network credentials on Windows 10 [Best solutions] (windowsreport.com)
It was solution 3 that worked for me. My user name to connect to ‘neilspc’ is ‘neilspcneil’, with no slashes and no colons.