Looking for Android feature promo integration to our existing app

We have an existing Android Application & Backend APIs in PHP which we wanted to add promo code integration and referrals. Only android to be done for the below changes. Just needed a update on the promos & refferals integration to the current application. 1. Integrate contacts to refer application. Call the API that user have reffered a contact 2. On booking check for any promo(if user have inputted) then have to call the discount API and apply the discount or any referral discount available to apply for the booking. 3. As above promo code integration. 4. There is a small calculation bug which will be a 1 hour task.