Do server to server calls support grpc?

I want the unreal engine game server to send messages to nakama

First: Is it possible to use unreal engine nakama plugin for server to server calls on nakama?

My guess is no because I am guessing server to server calls are curl only.

But if it is possible what is the method? I tried using the following which circumvents client authentication but it failed

NakamaClient = UNakamaClient::CreateDefaultClient(Config.ServerKey, Config.Host, Config.Port, Config.bUseSSL, Config.bEnableDebug);
NakamaRealtimeClient = NakamaClient->SetupRealtimeClient();
OnReceivedMyTestRPC.AddDynamic(this, &UNakamaSubsystem::OnMyTestRPCSuccess);
OnReceivedMyTestRPCFail.AddDynamic(this, &UNakamaSubsystem::OnMyTestRPCFail);
NakamaRealtimeClient->RPC(TEXT("myTest_lua"), TEXT("server rpc payload"), OnReceivedMyTestRPC, OnReceivedMyTestRPCFail);

Second: Is it possible to use grpc for server to server calls in general? if so do I need to do anything special? or is it just researching and implementing grpc in lua?

Hello @alireza,

You should be able to make S2S calls using this function: nakama-unreal/Nakama/Source/NakamaUnreal/Public/NakamaClient.h at master · heroiclabs/nakama-unreal · GitHub.