'customer_no' => array (
'datatype' => 'VARCHAR',
'formtype' => 'TEXT',
'validators' => array ( 0 => array ( 'type' => 'UNIQUE',
'allowempty' => 'y'),
'default' => '',
'value' => '',
I found this in the client.tform.php. I can add clients threw the controlpanel and leave the customer number empty. But threw the API I cant leave it empty.
I think there is a problem with 'type' => 'UNIQUE', because I can add the first client threw the api by leaving the customer number empty. But if I want to add a second client with leaving the customer number empty I get the error message.