Accessing a Custom Field when creating a Task with Zoho Projects API

We've created a custom field called Target Date through the Zoho Projects Portal, and are now trying to access that field with information I'm passing to it.

First we thought just formatting it as a JSON string by hand would work, but it didn't so we looked into the structure more.
When we get the project details of a task that already includes a Task Date, we get this structure:

  'custom_fields' => 
    array (size=1)
      0 => 
        array (size=3)
          'column_name' => string 'UDF_DATE2' (length=9)
          'label_name' => string 'Target Date' (length=11)
          'value' => string '10-11-2019 08:00:00 AM' (length=22)

The example says to use UDF_CHAR1, so we tried that as well as the column_name attribute. We also tried naming the values of the array to what they should be, and conceivable different ways of formatting it.

This is the closest we've got, it doesn't add the Target Date but it at least doesn't break the rest of the task creation.

$targetDate = [
'UDF_DATE2'=>'10-17-2021 08:00:00 AM',
];
                        $result = $ZohoProject->createTask([
                                'name'=>$FeeBreakdownRow->Title,
                                'tasklist_id'=>$Parent->ZohoID,
                                'duration'=>$FeeBreakdownRow->Hours,
                                'description'=>$FeeBreakdownRow->Description,
                                'start_date'=>date('m-d-Y'),
                                'custom_fields[]' => json_include($targetDate),
                                'duration_type'=>'hrs',
                                'work_type'=>'work_hours',
                                'task_duration_as_work'=>'true',
                                'person_responsible'=>$ZohoProject->findUserIDFromEmail($FeeBreakdownRow->OwnerEmail),
                            ]);

And createTask:

  public function createTask($params=[],$projectID=''){
        $projectID  = ($projectID)?$projectID:$this->projectID;
        $default_params = array(
            'priority'=>'None',
            'authtoken'=>self::AuthToken(),
        );
        $url = self::BASE_URL.'/portal/'.$this->portalID.'/projects/'.$projectID.'/tasks/';
        //var_dump($params);
        return $this->parseResponse($this->doRequest($url,array_replace($default_params,$params),'POST'));
    }

If there was an example that used a date I'm sure I could figure out how it works, but right now I feel like we've guessed everything it can possibly be and haven't had any luck yet. An example, or some pointers on what I'm doing wrong would be very helpful. Thanks!