$fields = civicrm_api3('CustomField', 'get', [
'return' => ['column_name', 'custom_group_id.table_name'],
'data_type' => 'ContactReference',
$fields = civicrm_api3('CustomField', 'get', [
'return' => ['column_name', 'custom_group_id.table_name'],
'data_type' => 'ContactReference',