# gRPC Error: 12 UNIMPLEMENTED: unknown service x / Method not found

**Code:** `12 UNIMPLEMENTED` · **Category:** API · **Seen on:** REST API

The server doesn’t have the service or method the client called — proto mismatch, wrong package name, or calling the wrong server.

## Meaning

Fully qualified names (package.Service/Method) must match exactly. Outdated generated code, missing service registration on the server, or routing through a proxy to the wrong backend cause it.

## Common causes

- Client and server proto definitions differ
- Service not registered on the server
- Wrong package/service name
- Proxy routing to another service

## Quick fix

1. List services with grpcurl (reflection)
2. Regenerate client stubs from the same proto
3. Register the service in the server setup

## Detailed fix by platform

### Shell

1. 

```bash
grpcurl -plaintext localhost:50051 list
grpcurl -plaintext localhost:50051 describe orders.v1.OrderService
```


## How to diagnose

1. **Services** — Exposed list
2. **Protos** — Same version?
3. **Routing** — Correct backend?

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Source: [WhatIsMyError](https://whatismyerror.com/errors/api/grpc-unimplemented)