How do I update custom fields?
$contactdata = array(
custom_fields => [content => $row[1], id =>'3'],[content => $row[2], id =>'1'],[content => $row[3], id =>'15'],[content => $row[4], id =>'17']
);
$contact = $infusionsoft->restfulRequest('GET', "https://api.infusionsoft.com/crm/rest/v1/contacts/$contactid", ['contactid'=>$contactid, 'contact'=>$contactdata, 'update_mask'=>'custom_fields']);