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

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.