I've successfully configured Composer credentials with my Magento Key set using
composer.phar config http-basic.repo.magento.com <public_key> <private_key>
and have confirmed that auth.json is effectively updated in Magento root with my keys from Magento Marketplace.
composer.phar update --dry-run Loads repositories, Updates dependencies etc. with the only errors being some requested packages not being found, no probs, I'll get to them ...BUT credentials are fine.
Why when I run
bin/composer.phar install does Composer proceed to download the bulk of the required dependencies, but fail at this particular module?