Referral program for android app which developing using Java

Hi, We are developing android mobile app, in that we want to implement one referral plan. Points: 1. When some one register, they has to buy one product in our app, 2. then in next page 5 referral coupons will reflect, 3. that 5 coupons he can refer to any person, but the coupon can get redeem only once by any one person only.(so 5 coupons 5 members only can use) 4. How this redeem will happen - who has received code he will install the app and he also has to buy one product in our app, then coupon entering option will open. then he can enter the received coupon. 5. Then some bonus amount will get credited into referred person account(app account). ** so we have developed every thing but we got stuck to generate this 5 referral coupons, and redemption option. And we are developing app using Java and its a android app. ***** Please who know very well those person only apply, and I don't have much time so please mention the time that how fast you can do it (based on this i'll give the rating once completed) And no negotiation on amount, please mention the exact price of you. New persons also can apply, but if you have confident on doing this task within the accepted timeline then only apply. Please I am in urgency don't apply just like that. Just i am keeping the budget for posting, but I welcome the genuine quotes(price) for this task. And for this app we are using Firebase database. Thank you.