How to validate the input value in back-end system in fiori app?

Dear friends,

      I create a custom fiori app to creat sale order, when I input sold-to number I want to validate it's value in my back-end system then return a bunch value of ship-to number for user to select, so any suggestion about this case or is there any example about back-end validation of the front-end input value ?

Thanks for your sincerely answer!

Zhang