functions.php

<?php
/**
 * Custom PayPal Adaptive Payments args.
 *
 * @param array $args
 * @param WC_Order $order
 * @return array
 */
function custom_woocommerce_paypal_ap_payment_args( $args, $order ) {
	$args['receiverList'] = array(
		'receiver' => array(
			array(
				'amount' => '40.00',
				'email'  => 'your@email.com',
				// 'primary' => 'true' // use this only for Chained Payment.
			)
		),
		'receiver' => array(
			array(
				'amount' => '15.00',
				'email'  => 'receiver1@email.com'
			)
		),
		'receiver' => array(
			array(
				'amount' => '60.00',
				'email'  => 'receiver2@email.com'
			)
		)
	);

	return $args;
}

add_filter( 'woocommerce_paypal_ap_payment_args', 'custom_woocommerce_paypal_ap_payment_args', 10, 2 );