Before you can ask Siri to send cash or messages through third-party apps, you'll need to take an extra step.
When you install a new or updated app that promises to work with Apple's Siri voice assistant, the natural thing to do is fire up Siri and try it out.
Only, you'll quickly find either Siri has no clue what you're talking about, or it prompts you to give access to the app's information.
To save time, here's how to give Siri permission to use apps beforehand:
There you'll find a list of apps installed on your iOS device that will work with Siri. Enable the app or apps you want to use by sliding the switch to the On position, and then exit Settings.
The next time you use Siri, it should know exactly what you're asking for and interact with the given app.
For example, I can say, "Call an Uber" to Siri and then it walks me through the process of getting a car without ever launching the Uber app itself.
You can read more in Taylor Martin's guide to Siri's new superpowers in iOS 10.