First check the port. HTTP is 20001 and SOCKS5 is 20481. A line built with the wrong port looks like a dead address and is not one.
Then check the username and password on the line. If you changed the service password, the old line stops working immediately and the new one is the one that counts.
If the port and the password are right and it still does not answer, use the Replace button on that address's row. Replacement is free and allowed once per address every 24 hours.
Replacement only happens while the service is delivering. An expired service does not replace addresses: it delivers again once it is renewed.