The discord link is not expired, it is our official link and others are joining with it. I would look into other reasons you may be unable to join a server:
You have hit the server join limit (100 servers) and cannot join any more.
You are using a VPN and it is causing a glitch
Your account is in limited access mode due to suspicious activity on discord
You are in a country/State where age verification is required to join some servers
You are trying to join from an apple mobile device
You are in a location where they have implemented a required age verification before allowing you to join some servers and you haven't verified yet.