Yes, you may use and test FooEvents on a staging environment as long as it’s only used on one live production site at a time in the case of a single domain license.
When you are ready to go live, you simply need to update the website URL that is linked to your license in your FooEvents Account (‘License Key‘ tab) and copy and paste your existing key into the FooEvents license key field in the FooEvents plugin settings on your live production site.
This help doc explains how to create a FooEvents license key and setup automatic plugin updates: https://help.fooevents.com/docs/frequently-asked-questions/installation-setup/how-do-i-create-a-license-key-and-setup-automatic-plugin-updates/