How to fix the «The requested package mage2.pro/<name> could not be found in any version» issue

I am getting the error on step 8
Add Mage2.PRO packages to the Magento 2 root composer.json file31

Using the below command it is giving the error:
php composer.phar require --prefer-source mage2pro/stripe:*

on Step 6 : I have created the config.json in the root directory

It looks like you have a fault on the step 6 (declaring the Mage2.PRO repository to the Composer).

As the step 6 states, you should place the config.json file to the COMPOSER_HOME directory, not to the “root” (?!) directory.

thanks, but i was not able to locate the composer directory due to which it is causing.
now it is installed and checking its process.