magento2 – Magento 2 – How to install extension from via composer?

I bought a this extension from I tried to install it via composer like this:

composer require bsscommerce/customer-approval

But I get

(InvalidArgumentException) Could not find a matching version of
package bsscommerce/customer-approval. Check the package spelling,
your version constraint and that the package is available in a
stability which matches your minimum-stability (stable).

I also followed this documentation, but it does not help.