مشکل در وارد کردن مایگریشن ها

میخوام مایگریشن هایی که دارم رو اجرا کنم اما خطا میده و دلیلش هم نمیدونم چیه اگه کمک کنید به حلش ممنون میشم :

  Illuminate\Database\QueryException  : SQLSTATE[42000]: Syntax error or access violation: 1071 Specified key was too long; max key length is 1000 bytes (SQL: alter table `shoppingcart` add primary key `shoppingcart_identifier_instance_primary`(`identifier`, `instance`))

  at F:\laravel-project\digikala2\vendor\laravel\framework\src\Illuminate\Database\Connection.php:664
    660|         // If an exception occurs when attempting to run a query, we'll format the error
    661|         // message to include the bindings with SQL, which will make this exception a
    662|         // lot more helpful to the developer instead of just the database's errors.
    663|         catch (Exception $e) {
  > 664|             throw new QueryException(
    665|                 $query, $this->prepareBindings($bindings), $e
    666|             );
    667|         }
    668|

  Exception trace:

  1   PDOException::("SQLSTATE[42000]: Syntax error or access violation: 1071 Specified key was too long; max key length is 1000 bytes")
      F:\laravel-project\digikala2\vendor\laravel\framework\src\Illuminate\Database\Connection.php:458

  2   PDOStatement::execute()
      F:\laravel-project\digikala2\vendor\laravel\framework\src\Illuminate\Database\Connection.php:458

  Please use the argument -v to see more details.

و مایگریشنی هم که مشکل داره به شکل زیر است :

    public function up()
    {
        Schema::create(config('cart.database.table'), function (Blueprint $table) {
            $table->string('identifier');
            $table->string('instance');
            $table->longText('content');
            $table->nullableTimestamps();

            $table->primary(['identifier', 'instance']);
        });
    }