What am I doing wrong with gform_field_input?

Hello,

I'm trying to change the input name value on a list field that has only one column. The current input name is input_10[]. I'm trying to use the following:

function map_input($input, $field, $value, $lead_id, $form_id) {
 if($field["inputName"] == "input_10[]") {
  $input = '<input type="text" name="instruction[][description]" value="" tabindex="16" />';
 }
 return $input;
}
add_action("gform_field_input", "map_input", 10, 5);

Am I doing something wrong?