How can I stop purchases from a certain device?

It would depend on if the device is part of your Family Sharing plan and where you want to limit purchases. You can use Screen Time & Contents & Restrictions to limit purchase in iTunes, Apps, in-App Purchases, and Wallet. Review these articles on setting up Family Sharing and also Parental Controls to see if this does what you need.

Set up Family Sharing - Apple Support

Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support