The «European Central Bank Currency Converter» extension for Magento 2 retrieves currency exchange rates from the European Central Bank as a more reliable alternative to the built-in Magento WebserviceX.NET currency converter, which sometimes does not work (see also the issue 2757).
The module is free and open source.

How to install

Hire me in Upwork, and I will:

• install and configure the module properly on your website
• answer your questions
• solve compatiblity problems with third-party checkout, shipping, marketing modules
• implement new features you need

2. Self-installation

bin/magento maintenance:enable
rm -f composer.lock
composer clear-cache
composer require mage2pro/currency-convert:*
bin/magento setup:upgrade
bin/magento cache:enable
rm -rf var/di var/generation generated/code
bin/magento setup:di:compile
rm -rf pub/static/*
bin/magento setup:static-content:deploy -f en_US <additional locales>
bin/magento maintenance:disable

How to update

bin/magento maintenance:enable
composer remove mage2pro/currency-convert
rm -f composer.lock
composer clear-cache
composer require mage2pro/currency-convert:*
bin/magento setup:upgrade
bin/magento cache:enable
rm -rf var/di var/generation generated/code
bin/magento setup:di:compile
rm -rf pub/static/*
bin/magento setup:static-content:deploy -f en_US <additional locales>
bin/magento maintenance:disable