call method
Implementation
Future<Map<String, dynamic>> call(Map<String, dynamic> payload) async {
AtRpcReq request = AtRpcReq.create(payload);
completerMap[request.reqId] = Completer();
logger.info('Sending request to $serverAtsign : $request');
await rpc.sendRequest(toAtSign: serverAtsign, request: request);
return completerMap[request.reqId]!.future;
}