To lock purchases on a PlayStation 4 (PS4), you can follow these steps:
1. Go to the main menu of your PS4 and select "Settings."
2. In the settings menu, scroll down and select "Parental Controls/Family Management."
3. If you haven't set up parental controls before, choose "Family Management" and follow the prompts to create a family.
4. Once you have set up family management, select the user for whom you want to enable purchase restrictions.
5. Choose "Parental Controls" and enter your password or passcode if prompted.
6. Under the "Restrict Use of PS4 Features" section, select "Application" and then "Set Features Available in Rest Mode."
7. In this menu, you will find options to restrict different features. To block purchases, make sure "Shopping" is unchecked.
8. Exit the menu and test the changes by trying to make a purchase on your PS4. It should ask for the password or passcode before proceeding.
By following these steps, you will be able to lock purchases on your PS4, preventing unauthorized purchases or unintended transactions.