Promo Codes

Question

I wish to know that how promo code works. What type of language used to make a promo code and how it is known that the code is expired or not.

Answer 1

Promo codes are the codes given by developers to promote on google play to use it freely

Answer 2

Like for instance I'm going to buy a course on udemy or buy something on e-commerce site. During checkout there is an option of applying coupons. I'm talking about that coupons. How they help in a discount or in for free. How these things work.

Answer 3

://promo code can you please explain it more