Laravel notification via method changes not coming in toMail method

I have one class where I calculate variables in via method and the same variable I want to use in toMail method but it's always null in the toMail Method. any idea why?

class FinancialQuestionnaireSubmissionNotification extends Notification implements ShouldQueue
{
    use Queueable,SerializesModels, GlobalMailHelperTrait;

    public Lead $lead;
    public $code;

    public function __construct(Lead $lead)
    {
        $this->lead = $lead->fresh();         
                          
    }
    public function via($notifiable)
    {

        $this->code = 'xyz';            
       
        return ['mail'];
    }
    /**
     * Get the mail representation of the notification.
     */
    public function toMail($notifiable)
    {                    
        dd($this->code);
    }   

    /**
     * Get the array representation of the notification.
     */
    public function toArray($notifiable)
    {
        return [
            //
        ];
    }
}

here my $this->code is always null why even after setting that variable in via method!

via Chebli Mohamed