Prevent Duplicate Purchases

function pw_edd_prevent_duplicate_purchase( $valid_data, $posted ) {

	$cart_contents = edd_get_cart_contents();

	foreach( $cart_contents as $item ) {

		if( edd_has_user_purchased( get_current_user_id(), $item['id'] ) ) {

			edd_set_error( 'duplicate_item', 'You have already purchased this item so may not purchase it again' );

		}

	}

}

add_action( 'edd_checkout_error_checks', 'pw_edd_prevent_duplicate_purchase', 10, 2 );