Put method yields HTTP 405 (method not allowed) but works in Postman (HTTP 500)...

Dear Sparkers,

I have created an addition to the profile settings page in Spark. The vue code:

Vue.component('update-mail-settings', {
   props: ['user'],

   data() {
       return {
           form: new SparkForm({
               type: ''
           })
       };
   },

   mounted() {
       this.form.mailsettings = this.user.mailsettings;
   },

   methods: {
       update() {
           Spark.put('update-mail-settings', this.form)
               .then(response => {
                   Bus.$emit('updateUser');
               });
       }
   }
});

I've created a route:

Route::put('/update-mail-settings', 'SettingsController@updateMailSettings');

and the Controller to handle the request. I disabled CSRF checking and as can be seen in the code beneath, also the auth middleware:

class SettingsController extends Controller
{
  
  public function __construct(){
    //$this->middleware('auth');
  }
  
  public function updateMailSettings(Request $request)
  {
    $request->user()->forceFill([
      'mailsettings' => $request->mailsettings
      ])->save();
      
      return Redirect::back()->with('success', 'Successfully updated mailsettings');
    }
  }

I didn't show the blade with radio buttons but that doesn't seem like the source of the error. Interestingly, when I monitor the requests in my Nginx log files I see a 405 error if I click on the update button on the website but if I use Postman, it yields a 500 code (after which it fails since it cannot assign the mailsettings variable --> "Call to a member function forceFill() on null")

Anyone have any idea?