Looking at your PHP snippet the problem is JSON strings should be enclosed with double quotes " rather than single quotes '
e.g. as follows:
<?
$guid="GUID_HERE";
$firstpassword="PASSWORD_HERE";
$secondpassword="PASSWORD_HERE";
$fee = "100000";
$amounta = "10000000";
$amountb = "400000";
$addressa= "1A8JiWcwvpY7tAopUkSnGuEYHmzGYfZPiq";
$addressb= "1ExD2je6UNxL5oSu6iPUhn9Ta7UrN8bjBy";
$recipients = urlencode('{
"'.$addressa.'": '.$amounta.',
"'.$addressb.'": '.$amountb.'
}');
echo 'Here';
$json_url = "
http://server2.blockchain.info/merchant/$guid/sendmany?password=$firstpassword&second_password=$secondpassword&recipients=$recipients&shared=$
$json_data = file_get_contents($json_url);
echo 'Response ' . $json_data . "\n";
$json_feed = json_decode($json_data);
$message = $json_feed->message;
$txid = $json_feed->tx_hash;
?>
Response:
{"message":"Sent To Multiple Recipients","tx_hash":"ccad4e724c665ee3c9118ade4277d9ac5a32a12e0e1a570b57263c8fc7b1367f"}
----
The reality is if you want top notch tech support then you need to pay for it, blockchain's APIs are free.