How do I set the old() value of a form_dropdown in Codeigniter 4? - codeigniter

Question

I've got a form in Codeigniter 4 and I'm using the form helpers to build the form.
When I use a form_input I can reload the submitted values of the form using the old() method. Like below.
<span class="input-group-text" id="inputGroup-sizing-sm">Membership Number</span>
<?php
$current_membership_options = [
'id' => "membership_number",
'name' => "membership_number",
'class' => "form-control",
'type' => 'text'
];
echo form_input($current_membership_options, old('membership_number'))
?>
I've tried a couple of different options but I can't get it to repopulate with a form_dropdown.
THE VIEW
<span class="input-group-text" id="inputGroup-sizing-sm">Membership Type</span>
<?php
$membership_type_option = [
'id' => 'membership_type',
'name=' => 'membership_type',
'class' => 'form-select ',
'type' => 'text'
];
echo form_dropdown($membership_type_option, $membership_type, old('membership_type'));
?>
I get $membership_type from the user controller.
public function new(): string
{
$user = new User;
$data = $this->model->getMemberships();
return view('Admin/Users/new', [
'user' => $user,
'membership_type' => $data
]);
}
And the model
/**
* #throws Exception
*/
public function getMemberships(): array
{
$result = $this->db->query('select * from membership_type')->getResultArray();
$dropdown = array();
$dropdown['0'] = 'Please Select';
foreach ($result as $r)
{
$dropdown[$r['id']] = $r['type'];
}
return $dropdown;
}
Thanks in advance.