Shopify sucks. Change my mind.

"The Postmates app is no longer available for download. If you already have the Postmates app installed, you can continue using it until January 10, 2019."

So, if your client built their site so that it depended on this app for a big requirement in their online store fulfillment, you now have to hope that there's another app that could match its capabilities. Or, you have to spend more budget to develop your own so you have 100% control over it.