504: Gateway Timeout
Likely cause
The origin's own upstream — not Cloudflare — timed out responding.
Check
Check the origin's own proxy/load balancer logs for which upstream call timed out, and check that dependency's own performance (e.g. a slow database query or internal API call).
Fix
Optimize or fix the slow upstream dependency, or increase the origin's own upstream timeout if the slow response is expected and acceptable.
Verify
Retry the request and confirm it completes within a normal time.