Fix for Recurring EDD Payments with Discounts (Paypal).

functions.php

<?php

// filter paypal because of discount
function sa_mod_paypal_gateway_data( $paypal_args = array(), $purchase_data = array() ) {
	if ( isset( $paypal_args['cmd'] ) && $paypal_args['cmd'] == '_xclick-subscriptions' ) {
		$paypal_args['sra'] = '3'; // change failed attempts.
		if ( $paypal_args['a3'] < 0.00 && isset( $purchase_data['discount'] ) ) {
			// Fix recurring amount
			$paypal_args['a3'] += $purchase_data['discount'];
			// fix single item, it matches the recurring amount.
			$paypal_args['amount_1'] += $purchase_data['discount'];
			// Add the discount
			// $paypal_args['discount_amount_cart'] = $purchase_data['discount']; 
		}
	}
	return $paypal_args;

}
add_filter( 'edd_paypal_redirect_args', 'sa_mod_paypal_gateway_data', 100, 2 );