PHP API - Custom Fields value not submitting

I am using asana php api and all working fine. But now i want to submit custom field value. I have created custom field in particular asana project. But when I am trying to submit through API, it is not submitting. I am not sure what should pass as parameter in php API. Below is custom field ids:

// documentos - 227624521239196
// Amortização - 320114643060735

And below is my api code:

$custField = array(“documentos” => “Amortização”);

$result = $asana->createTask(array(
‘workspace’ => ‘xxxxxxxxxx’,
‘custom_fields’ => $custField,
‘name’ => ‘xxxxxx’,
‘notes’ => ‘xxxxx’,
‘tags’ => ‘xxxxxx’,
‘due_on’ => ‘xxxxxx’,
‘assignee’ => ‘xxxxxxx’,
‘followers’ => ‘xxxxxx’


The structure of your custom_fields is wrong, you need to pass couples of id-value.