Gravity Forms: Assign unique ID to form

functions.php

add_action('gform_after_submission_3', 'we_add_submission_id', 10, 2);
/**
 * Assign unique ID to the Service & Support form, for Request Number
 */
function we_add_submission_id($entry, $form) {
	global $wpdb;
	$field_number = 14;
	$SubmissionID = 'S-' . $entry['id'];

	$wpdb->insert("{$wpdb->prefix}rg_lead_detail", array(
		'value'			=> $SubmissionID,
		'field_number'	=> $field_number,
		'lead_id'		=> $entry['id'],
		'form_id'		=> $entry['form_id']
	));
}