This filter lets you modify the data sent to Zapier when using Caldera Forms Zapier.
Send PayPal Transaction ID To Zapier
Send All PayPal Data To Zapier
Where Does This Code Go?
When using WordPress hooks to customize Caldera Forms or other plugins you should not modify the plugin files, or you will lose your changes when you update the plugin. Instead you should create a small plugin to hold the custom code. It's easy, learn how here.
Technically you can add the custom code to your theme's functions.php, but then you will not be able to change your theme and keep these customizations.