title: Prestashop - Check external ERP in Process Carrier
body: <p>I am a beginner in prestashop, and would like to be able to execute some php code in the moment in which the client gives the button "process cart" to make the order.</p>
  
  <p>This php code would call my server (ERP) to check if the products of the order are in stock or not, and in case NO, return false, to be able to display an error message and not continue the order until remove the products that are not stock ...</p>
  
  <p>I do not know which solution is better, if I override the present functions of my theme, or create my own module and make use of the hooks (but in this case I do not find that Hook would be required)</p>
  
  <p>I would appreciate that you recommend the best solution, and if you use hooks, which hook you could use.</p>
  
  <p>Thanks for everything,</p>
  
  <p>Regards.</p>