Thanks, @MerakiJockey505. I actually figured out my issue after finding this article: https://documentation.meraki.com/MX-Z/Client_VPN/Troubleshooting_Client_VPN#Windows_Error_789 - My upstream firewall was blocking port 4500 outbound. I also realized that I typed the number of the error incorrectly! It's Windows Error 789 (not 798).
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