Laravel Redirect to Login page after Post Request

I am inserting a form data into a database, after successful submission I want to redirect to the leads page.

HTML Form:

<form method="post" action="{{url('lead-message')}}">
     {{csrf_field()}}
     <input type="hidden" name="lead_id" value="{{$leads->id}}">
     <div class="form-group">
         <label for="exampleFormControlTextarea1">Type your message*</label>
         <textarea class="form-control" name="lead_message" id="lead_message" rows="3" value="" required></textarea>      
     </div>
     <button type="submit" class="btn btn-primary">Send Message</button>
</form>

Route:

Route::group( ['middleware' => ['auth', 'phoneverified']], function() {
    Route::resource('leads', 'LeadsController');
});

Controller:

public function leadMessage (Request $request) {
    $validate = $request->validate([
    'lead_message' => 'required',
    ]);

    $storeMessage = new LeadMessage;
    $storeMessage->lead_id = $request->lead_id;
    $storeMessage->message = $request->lead_message;
    $storeMessage->save();

    Session::flush('success', 'Message sends successfuly!');
    return redirect('leads/'.$request->lead_id);
}

But after successful submission, it redirects to the login page instead of the leads page and when I logged in again, it directly redirects me to the leads page.

I don't know where I am going wrong. I would appreciate any help in this regard.

you should use Session::flash('success', 'Message sends successfuly!'); instead of Session::flush('success', 'Message sends successfuly!'); because Session::flush()destroys your session. for more see documentation