When you install some new extension package in Magento 2 via the composer you can get an error:
Package vendor/module-name exists in composer repo (https://repo.packagist.org) and composer repo (https://repo.magento.com) which has a higher repository priority. The packages with higher priority do not match your constraint and are therefore not installable. See https://getcomposer.org/repoprio for details and assistance.
This error message is self-explaining and contains a link to the composer documentation.
The problem is that a module you try to install has an old version in the Magento composer repository and a new version in the free public packagist.org repository. However, the Magento repository has a higher priority and that is why composer cannot install the latest version and throws this error.
What you need to do to solve the issue is to:
1. Open composer.json file in your Magento 2 root directory.
2. Find the "repositories" section.
3. Replace the following code
with this one
Basically, you need to give the Magento repository not topmost priority.
4. Save the changes and try to install Magento 2 extension again.