You can require a password for every purchase or require a password every 15 minutes.
You can choose how often you want to enter your password when you buy items (including in-app purchases) from the App Store and other Apple services:
Always Require — Every time you make a purchase, you’ll be asked to enter your password, even if you’re signed in to your Apple Account.
Require After 15 Minutes — If you entered your password within the last 15 minutes, you won’t be asked to enter your password again.
If you don’t want to enter a password when you download free items, follow the steps below and turn off password protection for free items.
Open the Settings app.
Tap [your name].
Tap Media & Purchases.
Tap Password Settings, then choose the setting that you want.
If you don’t see Password Settings, you’ve already turned on Face ID or Touch ID for purchases. To change this, go back to Settings, tap “Face ID & Passcode” or “Touch ID & Passcode”, then turn off Face ID or Touch ID next to iTunes & App Store.
On your Mac, choose Apple menu () > System Settings.
Click [your name].
Click Media & Purchases.
Select the settings that you want for free downloads and purchases. If you have Touch ID turned on for purchases, you won’t see this menu.
From the Home screen, select Settings.
Select Users and Accounts.
Select [your name]’s Account.
Under Require Password, choose the settings that you want for purchases and free downloads.
You can’t completely turn off password protection for paid items on your iPhone, iPad, or computer. On Apple TV, you can turn off password protection for both free and paid items.
If you enabled Touch ID or Face ID for purchases in the App Store and other Apple services, you’ll be asked to use Touch ID or Face ID for every download, even if the item is free.
If you use Family Sharing, you can use Ask to Buy to control what kids buy. When a child asks to buy an item or download a free item, the family organizer can approve or decline the request.