civicrm_create_contact does not recognize date format

Assume custom_3 is a date field, you can test by running a script similar to the below. Put the script in bin/createContact.php and test it

<?php

$params = array( 'contact_type' => 'Individual',
'first_name' => 'Chris'
'last_name' => 'Amy',
'custom_3' => '20030120000000' );

require_once '../civicrm.config.php';
require_once 'api/v2/Contact.php';
$result = civicrm_contact_add( $params );
CRM_Core_Error::debug( $result );