IHttpRequest not POSTing anything

Okay I’ve tried everything and I still can’t figure this out. I have this method here, which converts @param keys and @param values into key/value pairs in a JSON object and is supposed to post it to @param URL:

void ASteamHandler::sendPostRequest(FString URL, FString eventKey, TArray<FString> keys, TArray<FString> values)
	TSharedPtr<FJsonObject> JsonObject = MakeShareable(new FJsonObject());

	activeEventKey = eventKey;
	for (int i = 0; i < keys.Num(); i++)
		FString key = keys*;
		FString value = values*;

		JsonObject->SetStringField(key, value);

	FString OutputString;

	TSharedRef<TJsonWriter<TCHAR>> JsonWriter = TJsonWriterFactory<TCHAR>::Create(&OutputString);
	FJsonSerializer::Serialize(JsonObject.ToSharedRef(), JsonWriter);

	TSharedRef<IHttpRequest> HttpRequest = FHttpModule::Get().CreateRequest();
	HttpRequest->SetHeader("Content-Type", "application/json");
	HttpRequest->OnProcessRequestComplete().BindUObject(this, &ThisClass::OnResponseReceived);

	GEngine->AddOnScreenDebugMessage(-1, 15.0f, FColor::Red, OutputString);
	UE_LOG(LogTemp, Warning, TEXT("%s"), *OutputString);

As you can see, I log the JSON object out at the end of the method. I can confirm that the JSON object is being created properly, and that all of the information is correct; however, according to my server, nothing is POSTed at all. $_POST is just an empty array.

Am I missing something?