Hey Arley,
Thank you for reaching out to us!
What I mentioned to Meesha is that If you want to use Event Tickets Plus on your staging wpengine hosted site, you don’t actually need to include a serial key/migrate your license from production site. For your staging site, you can download and install the latest release (from your downloads section) and ignore any warning messages.
Bear in mind that with this method you won’t receive any automatic plugin updates in your staging site (you’ll have to update all premium plugins manually).
I hope this helps! If you have any other questions, please open a new topic for further assistance.
Thanks,
Patricia