Authentication failed
The address exists. What failed was the username, the password or the IP.
Error 407 arrives when the address answered and refused the identification. The connection is up; what is missing is proof that it is yours.
The three places this breaks
The username has to be the one chosen in the order, 3 to 20 letters and numbers, no spaces. The password is the connection password, which is not the account password. And if you authorized by IP, the IP you have now has to be the authorized one: a connection that changes address breaks this without warning.
Changing the service password generates a new one, shows it once and does not touch the addresses. The username stays the same.