Undefined class constant 'SQLSRV_ENCODING_SYSTEM'

when trying to run php artisan migrate on laravel i'm getting the error

In database.php line 79:
Undefined class constant 'SQLSRV_ENCODING_SYSTEM'

i have the sql drivers etc installed but unsure how to solve this problem

database.php file

'sqlsrv' => [
        'driver' => 'sqlsrv',
        'host' => env('DB_HOST', 'localhost'),
        'port' => env('DB_PORT', '1433'),
        'database' => env('DB_DATABASE', 'forge'),
        'username' => env('DB_USERNAME', 'forge'),
        'password' => env('DB_PASSWORD', ''),
        'charset' => 'utf8',
        'prefix' => '',
        'options' => [PDO::SQLSRV_ENCODING_SYSTEM => false], // Used for MSSQL encoding
    ],

via Chebli Mohamed