Error 4600 Unable to process your request. Please verify if the name and value is appropriate for the "xmlData" parameter.

Hi, I'm trying to insert records in the Contacts module, but all I get is this 4600 Error. I've tried inserting just First Name and Last Name, but the error is still there, so I think is not related with my fields.
This is my code:

<?php

$url = 'https://crm.zoho.com/crm/private/xml/Contacts/insertRecords';

//campi contatto: riempire con i valori reali
$name = 'name';
$id_facebook = '0';
$username = 'user@mail.ext';
$password = 'encryptedpass';
$surname = 'surname';
$data_di_nascita = '2/6/1983';
$datanascita = '2';
$mesenascita = '6';
$annonascita = '1983';
$sesso = '1';
$lingueparlate = 'italiano';
$cf = 'xxxxxxxxxxxxxx';
$email = 'user2@email.ext';
$nickname = 'nick';
$aboutme = 'descrizione';
$telephone= 'xxxxxxxxxx';
$id_profile = '0';
$id_category = '0';
$paypal = 'paypal@mail.ext';
$nomebanca = 'banca';
$beneficiario = 'beneficiario';
$bankholder = 'bholder';
$partita_iva = 'xxxxxxxx';
$iban = 'xxxx';
$bic = 'xxxx';
$code = 'xxxxx';
$is_abil = '0';
$indirizzo = 'via...';
$citta = 'Roma';
$provincia = 'Roma';
$paese = 'Italia';
$cap = 'xxxxx';
$fax = 'xxxxxxxxxx';
$pi = 'xxxxxxxxxxx';
$indirizzofatt = 'via...';
$cittafatt = 'Roma';
$provinciafatt = 'Roma';
$paesefatt = 'Italia';
$contratto_partner_accettato = '0';
$codicesconto = 'xx';
$verifica_email = '1';
$verifica_telefono = '1';
$id_mmk = '0';
$tokenpass = 'xxxxxxxxx';

//fine campi. non editare oltre questa linea

$params = 'authtoken=myrealtoken&scope=crmapi&xmlData=';
$params .= '<Contacts><row no="1">';
$params .= '<FL val="First Name">'.$name.'</FL>';
$params .= '<FL val="Last Name">'.$surname.'</FL>';
$params .= '<FL val="id_facebook">'.$id_facebook.'</FL>';
$params .= '<FL val="password">'.$password.'</FL>';
$params .= '<FL val="id_profile">'.$id_profile.'</FL>';
$params .= '<FL val="id_category">'.$id_category.'</FL>';
$params .= '<FL val="is_abil">'.$is_abil.'</FL>';
$params .= '<FL val="Contratto Partner Accettato">'.$contratto_partner_accettato.'</FL>';
$params .= '<FL val="Verifica Email">'.$verifica_email.'</FL>>';
$params .= '<FL val="Verifica Telefono">'.$verifica_telefono.'</FL>';
$params .= '<FL val="Mailing Street">'.$indirizzo.'</FL>';
$params .= '<FL val="Mailing City">'.$citta.'</FL>';
$params .= '<FL val="Mailing Zip">'.$cap.'</FL>';
$params .= '<FL val="Mailing Country">'.$paese.'</FL>';
$params .= '<FL val="Description">'.$aboutme.'</FL>';
$params .= '<FL val="Secondary Email">'.$email.'</FL>';
$params .= '<FL val="Data Di Nascita (text)">'.$data_di_nascita.'</FL>';
$params .= '<FL val="Data Nascita">'.$datanascita.'</FL>';
$params .= '<FL val="Mese Nascita">'.$mesenascita.'</FL>';
$params .= '<FL val="Anno Nascita">'.$annonascita.'</FL>';
$params .= '<FL val="Lingue Parlate">'.$lingueparlate.'</FL>';
$params .= '<FL val="Codice Fiscale">'.$cf.'</FL>';
$params .= '<FL val="nickname">'.$nickname.'</FL>';
$params .= '<FL val="Nome Banca">'.$nomebanca.'</FL>';
$params .= '<FL val="beneficiario">'.$beneficiario.'</FL>';
$params .= '<FL val="Bank Holder">'.$bankholder.'</FL>';
$params .= '<FL val="iban">'.$iban.'</FL>';
$params .= '<FL val="bic">'.$bic.'</FL>';
$params .= '<FL val="Partita Iva">'.$pi.'</FL>';
$params .= '<FL val="sesso">'.$sesso.'</FL>';
$params .= '<FL val="username">'.$username.'</FL>';
$params .= '<FL val="Indirizzo Fatturazione">'.$indirizzofatt.'</FL>';
$params .= '<FL val="Città Fatturazione">'.$cittafatt.'</FL>';
$params .= '<FL val="Provincia Fatturazione">'.$provinciafatt.'</FL>';
$params .= '<FL val="Paese Fatturazione">'.$paesefatt.'</FL>';
$params .= '<FL val="Phone">'.$telephone.'</FL>';
$params .= '<FL val="Fax">'.$fax.'</FL>';
$params .= '<FL val="Paypal Business Email">'.$paypal.'</FL>';
$params .= '<FL val="code">'.$code.'</FL>';
$params .= '<FL val="Id mmk">'.$id_mmk.'</FL>';
$params .= '</row></Contacts>';
print_r($params);
$ch = curl_init();
curl_setopt($ch,CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 1);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_TIMEOUT, 30);
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch,CURLOPT_POSTFIELDS, $params);
$result = curl_exec($ch);
print_r(curl_error($ch));
print_r($result);
curl_close($ch);
?>;

This is the result page (with params variable printed):

authtoken=myrealtoken&scope=crmapi&xmlData=<Contacts><row no="1"><FL val="First Name">name</FL><FL val="Last Name">surname</FL><FL val="id_facebook">0</FL><FL val="password">encryptedpass</FL><FL val="id_profile">0</FL><FL val="id_category">0</FL><FL val="is_abil">0</FL><FL val="Contratto Partner Accettato">0</FL><FL val="Verifica Email">1</FL>><FL val="Verifica Telefono">1</FL><FL val="Mailing Street">via...</FL><FL val="Mailing City">Roma</FL><FL val="Mailing Zip">xxxxx</FL><FL val="Mailing Country">Italia</FL><FL val="Description">descrizione</FL><FL val="Secondary Email"> user2@email.ext</FL><FL val="Data Di Nascita (text)">2/6/1983</FL><FL val="Data Nascita">2</FL><FL val="Mese Nascita">6</FL><FL val="Anno Nascita">1983</FL><FL val="Lingue Parlate">italiano</FL><FL val="Codice Fiscale">xxxxxxxxxxxxxx</FL><FL val="nickname">nick</FL><FL val="Nome Banca">banca</FL><FL val="beneficiario">beneficiario</FL><FL val="Bank Holder">bholder</FL><FL val="iban">xxxx</FL><FL val="bic">xxxx</FL><FL val="Partita Iva">xxxxxxxxxxx</FL><FL val="sesso">1</FL><FL val="username"> user@mail.ext</FL><FL val="Indirizzo Fatturazione">via...</FL><FL val="Città Fatturazione">Roma</FL><FL val="Provincia Fatturazione">Roma</FL><FL val="Paese Fatturazione">Italia</FL><FL val="Phone">xxxxxxxxxx</FL><FL val="Fax">xxxxxxxxxx</FL><FL val="Paypal Business Email"> paypal@mail.ext</FL><FL val="code">xxxxx</FL><FL val="Id mmk">0</FL></row></Contacts> 4600Unable to process your request. Please verify if the name and value is appropriate for the "xmlData" parameter. ;

The strange thing is that if I take the generated url and attach it to https://crm.zoho.com/crm/private/xml/Contacts/insertRecords? the record is added. Any help is appreciated