Softon\Indipay is not instantiable while building

I received this message when i try to instantiate Soften\Indipay on Laravel 5.4* github

Target [Softon\Indipay\Gateways\PaymentGatewayInterface] is not instantiable while building [\Softon\Indipay\Indipay].

i registered it in the app/config.php but it doesn't work, how can i fix it ?

'providers' => [
    ....
    Softon\Indipay\IndipayServiceProvider::class,
    ....
];

Thank you.

via Hesham AbdAllah