Is there any way to sell something online,if you don't have a credit card?

PayPal.

My country is not supported by them
https://developer.paypal.com/docs/classic/api/country_codes/

It may be helpful to mention where you are…

I live in Pakistan and it is technologically,a very much underdeveloped country (in reality).

You need a bank account that can receive payments from over seas, but payments to Pakistan are incredibly problematic for the rest of the world. It would put me on a watch list where I live and payments could take over 15 days because of lack of infrastructure.

You can use Bitcoins.