# rpc error: code = Unimplemented desc = unknown service pb.OrderService

- **ID:** `go/grpc-unimplemented-unknown-method`
- **Domain:** go
- **Category:** module_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

The client is calling a fully-qualified service name that the server does not have registered. Usually caused by mismatched proto package/name between client and server, a stale generated stub, or registering the service under a different package path.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 1.x | active | — | — |

## Workarounds

1. **** (88% success)
   ```
   Confirm the registered service name on the server matches the client stub by inspecting the descriptor:

sd := pb.File_order_proto.Services().ByName("OrderService")
log.Println("service full name:", sd.FullName())
// ensure pb.RegisterOrderServiceServer(srv, impl) is called
   ```
2. **** (90% success)
   ```
   Regenerate stubs from the canonical .proto and share the exact module version between client and server:

// go.mod on both sides must reference the same generated module version
// buf generate / protoc --go_out=. --go-grpc_out=. order.proto
   ```

## Dead Ends

- **** — The server will never suddenly gain the method; retrying an unimplemented RPC always returns Unimplemented again. (97% fail)
- **** — The service name mismatch is independent of the network endpoint; a different port with the same stale stub fails identically. (85% fail)