This is an example of working with a hook that is triggered when an item is added to the cart via the addon WooCommerce Cart & Checkout Action

wc-action-add-to-cart.php

<?php

/**
 * This is an example of working with a hook
 * that is triggered when an item is added to the cart via the addon
 * @link https://jetformbuilder.com/addons/woocommerce-cart-checkout-action/
 * 
 * Works with both JetFormBuilder and JetEngine Forms
 */

add_filter( 'jet-form-builder/action/redirect_to_woo_checkout/add-to-cart', function ( $add_to_cart_data ) {
	/**
	 * @var array $cart_item_data
	 *
	 * $cart_item_data[ $manager->form_data_key ]       -> Form Request (array)
	 * $cart_item_data[ $manager->form_id_key ]         -> Form ID (int)
	 * $cart_item_data[ $manager->action_settings_key ] -> Current action settings (array)
	 *
	 * I strongly recommend not to change the $cart_item_data array.
	 * You can only get data from it.
	 */
	list( $product_id, $quantity, $variation_id, $variation, $cart_item_data ) = $add_to_cart_data;

	$manager = \Jet_FB_Woo\Plugin::instance()->wc;

	/**
	 * This is an example of how to change the quantity of an item
	 * based on the value from the form field.
	 */
	$request  = $cart_item_data[ $manager->form_data_key ];
	$quantity = $request['your_field_name'] ?? 1;

	return array( $product_id, $quantity, $variation_id, $variation, $cart_item_data );
}, 10 );