BAD_REQUEST_EXCEPTION when calling StartMatchBackfill on GameLift C++ SDK (Unreal Plugin)

Question

Hey, I'm trying to implement the manual backfill into my server. I'm using Unreal Engine 5.3 and the GameLift plugin for Unreal. Unfortunately when I call StartMatchBackfill I get a BAD_REQUEST_EXCEPTION error. I've tried checking if all the parameters were passed correctly with the VS debugger and they were (I've passed the m_matchmakingConfigurationArn, m_gameSessionArn and m_players; I have two players and m_players is passing m_playerId, m_team, m_playerAttributes and m_latencyInMs correctly. The only parameter missing is the ticket id which should be auto-generated by AWS. I've even tried adding it manually, but I'm getting the same error. 
I've also tried to start the match backfill on the AWS CLI using the parameters logged out by my game server and there it's working properly. So I don't know what to do now since I don't have more detailed informations about this BAD_REQUEST_EXCEPTION.
Thanks for your help!

EDIT: This is a screenshot of the outcome in the VS Debugger: ![Screenshot](/media/postImages/original/IM1xKeptJlS82QrokOGrRvow)

Jackson_AWS · Accepted Answer

Hey Scienziatogm, this doesn't solve your problem, but it might help your debugging since the logs aren't helpful at the moment. I've looked at the source code for the [5.1 C++ Server SDK](https://aws.amazon.com/gamelift/getting-started-sdks/) and it looks like the exception message is hard-coded to bad request at the path: `gamelift-server-sdk/source/aws/gamelift/internal/GameLiftServerState.cpp > Internal::GameLiftServerState::StartMatchBackfill`:
```
StartMatchBackfillOutcome
Internal::GameLiftServerState::StartMatchBackfill(const Aws::GameLift::Server::Model::StartMatchBackfillRequest &startMatchBackfillRequest) {
    if (AssertNetworkInitialized()) {
        return StartMatchBackfillOutcome(GameLiftError(GAMELIFT_ERROR_TYPE::GAMELIFT_SERVER_NOT_INITIALIZED));
    }

WebSocketStartMatchBackfillRequest request = Internal::StartMatchBackfillAdapter::convert(startMatchBackfillRequest);
    GenericOutcome rawResponse = m_webSocketClientManager->SendSocketMessage(request);
    if (rawResponse.IsSuccess()) {
        WebSocketStartMatchBackfillResponse *webSocketResponse = static_cast(rawResponse.GetResult());
        StartMatchBackfillResult result = Internal::StartMatchBackfillAdapter::convert(webSocketResponse);
        delete webSocketResponse;

return StartMatchBackfillOutcome(result);
    } else {
-->     return StartMatchBackfillOutcome(GameLiftError(GAMELIFT_ERROR_TYPE::BAD_REQUEST_EXCEPTION));
    }
}
```

`rawResponse` is a GenericOutcome which might have a GameLiftError of it's own. You could try updating that line to something like the following and see if you get a more useful error back:
```
    } else {
        return StartMatchBackfillOutcome(rawResponse.GetError());
    }
```

BAD_REQUEST_EXCEPTION when calling StartMatchBackfill on GameLift C++ SDK (Unreal Plugin)

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