Regist domain by php CURL(Errorcode:400)

When i use versio API and php CURL, the service return 400,the postDate in the demo
I refer to https://www.versio.nl/RESTapidoc/#api-Domains-List
running program, the domain registration has not been completed,and return a error code and message.
my demo

<?php
$post_a = array(
'contact_id'=>529254,
'years'=>1
);
$curl = curl_init();
curl_setopt($curl,CURLOPT_URL,'https://www.versio.nl/api/v1/domains/letone.be');
curl_setopt($curl,CURLOPT_RETURNTRANSFER,true);
curl_setopt($curl,CURLOPT_HTTPAUTH,CURLAUTH_BASIC);
curl_setopt($curl,CURLOPT_USERPWD,"myaccout:mypwd");
curl_setopt($curl,CURLOPT_SSL_VERIFYPEER,false);
curl_setopt($curl,CURLOPT_FOLLOWLOCATION,1);
curl_setopt($curl, CURLOPT_POST, 1);
curl_setopt($curl, CURLOPT_POSTFIELDS, $post_a);

$response = curl_exec($curl);
$data = json_decode($response);
print_r($data);


//the first run,and the return
//stdClass Object( [error] => stdClass Object ( [code] => 400 [message] => ObjectInvalid|Invalid years ameter )

//the The next run result has always been
//stdClass Object ( [error] => stdClass Object ( [code] => 400 [message] => ObjectNotAllowed|Domain registration already requested ) )