(421): 4.3.0 Upstream error even though everything is passing 🥲
I'm getting this error even though everything is passing and the link is useless 
Unknown error: transient error (421): 4.3.0 Upstream error, please check https://developers.cloudflare.com/email-routing/postmaster for possible reasons why. LfJLYFMzyUy9
Unknown error: transient error (421): 4.3.0 Upstream error, please check https://developers.cloudflare.com/email-routing/postmaster for possible reasons why. LfJLYFMzyUy9
Cloudflare Docs
Reference page with postmaster information for professionals, as well as a known limitations section.
