[ insertRecords ] Inserting boolean value with zoho crm API in XML

Hello,

i'm trying to insert some records in zoho from a php script.
It was ok before i tried to insert a boolean field.
Here is some xml code:

$xml =
.'<Accounts>'
   .'<row no="1">'
       .'<FL val="Account Name">Maxime</FL>'
       .'<FL val="Account Type">Particuliers</FL>'
       .'<FL val="Inscrit">true</FL>'
   .'</row>'
.'</'.$postParams['module'].'>';

the insertion works without the last field which is a boolean field in my zoho crm.
when i try to complete this field, the insert fails...

Can you tell me what is the way to complete boolean field via insertRecords method and XML ?

Thank you :)