This article outlines two use cases and actions to consider when using the Multi-Currency functionality.
Why are currencies not appearing on the website?
If a currency is not appearing on the website, the currency may not be assigned to the website. Check and ensure that the currency is in the assigned to the website within Websites > click Edit for the desired website > Currencies tab
Why are currency prices not changing?
Currency prices must be manually set within Configured Commerce in Administration > Currencies > click Edit for the desired currency > Rates; however, it is possible to set up an integration job to contact a currency rating service (such as WebserviceX). If the integration and settings have been set up, ensure that the integration job has also been set up correctly.