A few possibilities:
The URL link of discord invitation has expired.
Your IP is in the ban range from discord servers causing you trouble to join new servers.
You already participate in 100 servers, anything above 100 will display the error you received.
Either cookies or cache is preventing you from joining, in case you are trying to join the server using Web App login instead of Desktop Client login.
Still doesn't hurt for staff members to check whether you're blacklisted or not, post your Discord ID below or you can DM Ommadawn as he already gave you his Discord ID, good luck ~
