problem with "recur_amount"

Hi, I am testing recurring billing in php.

Here is my transaction array

[

"type"=>"res_purchase_cc",

"amount"=>"10.23",

"order_id"=>$this->orderId,

"cust_id"=>$this->customerId,

"crypt_type"=>"7"

]

Here is my recurring array

[

"recur_unit"=>"month",

"start_date"=> date('Y/m/d', strtotime('+1 year')),

"start_now"=>"true",

"period"=>"12",

"num_recurs"=>"10",

"recur_amount"=>"10.23"

];

For the test, I am using 4242424242424242

Here is the message that I get after I send the https request :

"Error unfinished element 'recur_amount"