Thanks for your question and interest in the delivery.com App Challenge!
Per the rule below, you must integrate the delivery.com API into your app.
"Create, develop and submit a working app that uses the APIs provided by Poster from time to time available at http://developers.delivery.com, allows users of delivery.com to order online from restaurants, wine and liquor stores and/or laundries and dry cleaners, and contains features designed to improve the user’s online ordering experience."
You may utilize additional data, APIs, or SDKs in your app. However, per the official rules your app "shall not utilize APIs from any third party that is engaged in the business of providing online ordering services for restaurants, laundries, dry cleaners, wine and liquor stores or similar businesses for any purpose whatsoever."