Not all apps integrated with Zapier will send through an email address as the owner field on events. If the app you'd like to integrate with MySpinify only sends user IDs, then we can still help you setup your Zap so it will work:
After you've created your users in MySpinify, create a spreadsheet with your user's user ids from the external integration in one column and their corresponding email address for their account in MySpinify in another column.
Then contact our support team via chat and attach the spreadsheet to the conversation. We can add the external users for you, and then they'll be ready to use with your integration.