Set the Default Redirect URL

functions.php

<?php // don't add this line since it's already in your functions.php file

function _si_redirect_url_meta_fields( $fields ) {
	if ( '' === $fields['payment_redirect']['default'] ) {
    $fields['payment_redirect']['default'] = 'http://yoursite.com/url/';
	}
	return $fields;
}
add_filter( 'si_redirect_url_meta_fields', '_si_redirect_url_meta_fields' );

This snippet is a customization for Sprout Invoices. A customizable solution that provides a way for you to get paid via your WordPress site. For more information please don't hesitate to reach out.