Hi there -
Based on my small business and entrepreneurial experience, here are a few suggestions to sell your patent on a game app:
*Flippa.com markets themselves as "the world’s number 1 destination for buying and selling online businesses." You can sell a website, or an app (patented or not, I believe) on the site. Visit: https://flippa.com/apps.
*GreyB provides intellectual property services and they have researched a guide to 20+ online marketplaces to buy and sell patents (https://www.greyb.com/marketplaces-buy-sell-patents/)
*And for what it is worth, Legal Zoom has an introductory article on "Selling Your Patent: What You Need To Know by Beverly Rice" (https://www.legalzoom.com/articles/selling-your-patent-what-you-need-to-know)
Best of luck & if you'd like to ask any follow up questions, feel free to schedule a call.