检测到laravel中fieldname的无效UTF-8

I am storing some response from a third party. Sometimes data is not storing in to database. I checked the Laravel log and getting some error. I am using laravel 5.5 and mongo db.

Any help world be appreciated. Thanks.

Laravel log

[2018-09-10 11:40:50] production.ERROR: Detected invalid UTF-8 for fieldname "shipping_city": München  
[2018-09-10 11:41:03] production.ERROR: Detected invalid UTF-8 for fieldname "_id": Ã$zjmêá¹ëmy×
[2018-09-10 11:48:16] production.ERROR: Method [error] does not exist on [App\Http\Controllers\PaymentController]. {"userId":"5b0d2b6f12236ca36a2282ed","exception":"[object] (BadMethodCallException(code: 0): Method [error] does not exist on [App\\Http\\Controllers\\PaymentController]. at /var/www/vhosts/cabin-holiday.frontend/vendor/laravel/framework/src/Illuminate/Routing/Controller.php:68)

PaymentController.php

$payment        = new Payment;

   foreach($_POST as $key => $value) {
     if(Schema::hasColumn($payment->getTable(), $key)){
        if(is_array($value)) {
           $payment->{$key} = $value[1];
        } else {
                $payment->{$key} = $value;
                }
      }
    }
$payment->save();

Couple of ways you can handle that. One of them is to use utf8-encode

string utf8_encode ( string $data )

PaymentController.php

$payment = new Payment;

   foreach($_POST as $key => $value) {
     if(Schema::hasColumn($payment->getTable(), $key)){
        if(is_array($value)) {
           $payment->{$key} = utf8_encode($value[1]);//changes
        } else 
        {
                    $payment->{$key} = utf8_encode($value);//changes

        }

        }
        }
    $payment->save();