[Refer A Friend] Set store credit reward to percentage of order subtotal i.e. excluding discounts

functions.php

<?php

add_filter( 'automatewoo/referrals/reward_amount', 'filter_automatewoo_referrals_reward_amount', 10, 3 );

/**
 * @param float $reward_amount
 * @param \AutomateWoo\Referrals\Advocate $advocate
 * @param \WC_Order $order
 * @return float
 */
function filter_automatewoo_referrals_reward_amount( $reward_amount, $advocate, $order ){
	if ( ! $order ) {
		return 0;
	}

	$reward_percentage = (float) AW_Referrals()->options()->reward_amount;
	return $order->get_subtotal() * $reward_percentage / 100; // subtotal excludes all discounts, fees and shipping
}