API: add order not insert all customfield

Hello,

We create a custom order form to our website using whmcs api, everything is fine, but in add order function two customfields field not inserting to whmcs system...

These two field not insterting:
$postfields["customfields"] = base64_encode(serialize(array("1"=>$_POST['subdomain'])));
$postfields["customfields"] = base64_encode(serialize(array("2"=>$_POST['emailad'])));

but the third customfield is inserted:
$postfields["customfields"] = base64_encode(serialize(array("3"=>$_POST['passw'])));

So, what's is the problem with the code?

Thanks,

G.