如何处理下一个请求而不等待先前请求的响应

i have a backend system using PHP to handle transaction. in this case, there is three environment involved. A = client, B = my system, C = payment gateway the scenario is :

  1. client (A) send request over HTTP post request,then
  2. my system (B) receive that request and then
  3. send request to payment gateway (C) using cUrl.

what happen now is : every request from client proceed by my system partially, which mean next process will be process when previous request to C has response.

what i want is : even the prevoius request not yet responded by C, my system can receive next request from A and send another request to C.