private async Task SendMessage(Message message, List <FileModel> attachments, Guid stamp)
{
var dto = Dto.CreateMessage(message, attachments);
var ack = Dto.CreateMessageAck(message, stamp);
await Task.WhenAll(
Clients.OthersInGroup($"R{message.RoomId}").SendAsync("NewMessage", dto),
Clients.Caller.SendAsync("MessageAck", ack)
);
}