Why can't my son sign in to Microsoft Family Features (single-use codes are supposedly incorrect)?

[Windows 11]

When my son tries to log in to his Microsoft account on his computer, the Microsoft Family Features pop-up window appears and asks him to sign-in to use family features. On the next screen, "Making sure it's you", he provides his PIN. The next screen reports, "Because you're accessing sensitive info, we'll send a code to **e-mail address** to verify your identity." He clicks "Send code", checks his e-mail, receives a message with the title "Your single-use code", finds the 6-digit code, enters it on the Family Features pop-up window, and the system responds with "That code didn't work. Check t

Continue reading...