Argo Tunnel customers are unable to create new tunnels, or reconnect existing tunnels.
Customers running cloudflared version 2019.11.2 or older must update to version 2019.11.3 or newer. The latest version of cloudflared is 2021.2.2, available here: https://github.com/cloudflare/cloudflared/releases
Customers running cloudflared version 2019.11.3 or newer - no action required. Cloudflare is restoring service for these versions over the course of the next few hours.