Having problems with helloworld.proto - basic failure

[suityou01]

If I use the compiler from the command line like so

protoc --php_out=./src/classes \
  --openswoole-grpc_out=./src/classes \
  --plugin=protoc-gen-grpc=protoc-gen-openswoole-grpc \
  ./proto/helloworld.proto

I get a basic error which doesn't give me much to go on

/usr/local/bin/protoc-gen-openswoole-grpc: 1: Syntax error: "(" unexpected
--openswoole-grpc_out: protoc-gen-openswoole-grpc: Plugin failed with status code 2.

If I omit the --openswoole-grpc_out switch it works

It appears it doesn't like something about the service def

syntax = "proto3";

package helloworld;

// The greeting service definition.
service Greeter {
  // Sends a greeting
  rpc SayHello (HelloRequest) returns (HelloReply) {}
}

service Stream {
  rpc FetchResponse (HelloRequest) returns (stream HelloReply) {}
}

// The request message containing the user's name.
message HelloRequest {
  string name = 1;
}

// The response message containing the greetings
message HelloReply {
  string message = 1;
}

Where am I going wtong?