Hi Tom,
I ran into this as well and learned the participants must first be included on an Invitation list - are you using a Cvent Confirmation # or invitation/Cvent ID. The steps I took were:
1) Import contacts to an Invitation List
2) Export invitation List to get the Cvent ID
3) Reformat Export to match the Participants template.
I had to open a help ticket to get the following steps as it was not clear in the instructions. We were adding back log of events that took place before our cvent usage.
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Amy Jackson
Director of Project Management
Blue River PetCareUnited States
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