This article may be outdated. Please reach out to Google support for questions around setting up your Adwords campaign.
First you need to set up a custom domain as described in the article below. This will allow you to match your display URL with your destination URL.
Getting Started With Your Google Adwords Campaign
Google will approve a destination URL that is a sub-domain of your display URL. They just want to make sure the top-level domain of yourdomain.com match for both display and destination.
Destination URL: promo.yourdomain.com/product
Display URL: yourdomain.com
An exception to this is if you're using a domain that hosts many different independent entities like blogspot.com or wordpress.com (blogspot.com as your display and myblog.blogspot.com as your destination would not be approved).
You can read a bit more about it in the Google help articles below
Campaign: set of ad groups that share a budget and settings such as location targeting.
Ad group: set of keywords, ads, and bids.
Destination URL: sub-domain of your display URL.
Destination URL match: your display URL and destination URL share the same domain.