Proto3 script for Gateway Request

Hello all,
I am trying to use gRPC to request all registered gateways list from a chirpstack server.
In chirpstack 3.0 it was clear for me how it is done.
In chirpstack 4.0 I have to use grpc protobufs a topic where I am completely new.
As a gRPC gui client I use BloomRPC.
I have managed to find an example but it does not work:

syntax = "proto3";

package chirpstackapi;

service GatewayService {
  rpc List (ListGatewayRequest) returns (ListGatewayResponse);
}

message ListGatewayRequest {
  int32 limit = 1;  // The maximum number of gateways to return.
  int32 offset = 2; // The offset for pagination.
}

message ListGatewayResponse {
  repeated Gateway gateways = 1; // The list of gateways.
}

message Gateway {
  string id = 1;          // The unique identifier of the gateway.
  string name = 2;        // The name of the gateway.
  string description = 3; // A description of the gateway.
}

I get: “error”: "12 UNIMPLEMENTED: "

The API token was generated from chirpstack.

What changes do I have to make in the proto3 script in order to make it work ?