I have getting 521 on my backend server , proxied from cloudflare

i have a python application that is running on my ec2 server , the server is running and i have used nginx to reverse proxy
my backend runs on my subdomain
api.xyz.fun which is configured correctly in cloudflare

it was working perfectly till yesterday , but today i am getting 521

my production is down in a early stage startup please help

Hey there!

Usually when you’re getting 521 it means we are having trouble connecting to your host. Do check with your hosting provider and origin logs to make sure everything is going well.

Otherwise, there’s a possibility it’s due to this: