In some cases you see this error message:
One or more validation errors occurred. (ValidationError) should have required property '640eda18f549b167ccdd6d48'; should have required property '640eda18f549b167ccdd6de5' (createEventParticipant)
Cannot create the participant
Resolution:
This error message means that each or one of the three mandatory fields is not available in the registration form:
1. First Name
2. Last Name
3. Email
When you update this and these fields to the registration form the issue is resolved