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

"type": "composer",
"url": "https://repo.magento.com/"

with this one

"type": "composer",
"url": "https://repo.magento.com/",
"canonical": false

Basically, you need to give the Magento repository not topmost priority.

4. Save the changes and try to install Magento 2 extension again.