How can I test my OFFER CODE in my development environment

I have a iOS mobile application where I am using OFFER CODES year by year where the users can login & re-new the subscription for the application.

I have finished my development in my Backend & my iOS Frontend side & I have tested both the platforms individually and they are in the working condition.

I need a way to test this after the integration using test flight with a verified application or using sandbox environment using my local application.

How can I test my OFFER CODE in my development environment
 
 
Q