inside config/services.php

add 
'openrouter' => [
        'api_key' => env('OPENROUTER_API_KEY'),
        'base_url' => 'https://openrouter.ai/api/v1/chat/completions',
    ],

----------------OR--------------------------

'openrouter' => [
        'key' => env('OPENROUTER_API_KEY'),
    ],
-------------------------------

add to your .env

OPENROUTER_API_KEY=your_api_key