Q: Invalid Account

If the account has been disabled for security reasons then resetting the password might fix it : If your Apple ID has been locked - Apple Support

You might then need to log out and back into your account wherever you're using it : What to do after you change your Apple ID email address or password - Apple Support

If that doesn't fix it then contact iTunes Support : https://www.apple.com/emea/support/itunes/contact.html

Resetting the password also applies to accounts that are disabled for security reasons - from that linked page :

If your Apple ID is locked for security reasons, you might see one of these alerts:

• “This Apple ID has been disabled for security reasons”
• "You can't sign in because your account was disabled for security reasons"
• "This Apple ID has been locked for security reasons"