520 Error; Malformed header: missing HTTP content-type with GRPC service

I have a grpc service that functions great with just DNS enabled.

However, whenever I enable the cloudflare CDN, I get the following error from grpcurl:

grpcurl -H domain:443 list                                                                                                                                                                                                                                                                                                                                                            
Failed to list services: rpc error: code = Unknown desc = unexpected HTTP status code received from server: 520 (); malformed header: missing HTTP content-type

I have verified:

  • Full TLS is enabled
  • GRPC is enabled in my domain network settings.

Is there any way I can debug what’s actually happening?

If I visit the page over HTTP, I also get the 520 error. However my application never receives any traffic.

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