Laravel passport installation error

For Laravel 5.3.

In your composer.json file put "laravel/passport": "~1.0" and run "composer update" command.

It happens, because after releasing Laravel 5.4, this package also had been updated to v 2.0 and requires Laravel 5.4. But you are using Laravel 5.3. Try to install earlier version:

composer require laravel/passport ^v1

Also, you can learn about the versions of this package here:

Laravel Passport