An upcoming maintenance period is planned for the Attendee Activities REST API endpoints. Any new Attendee Activities you try to create during this maintenance period will be queued and created after maintenance is complete.
The maintenance period is scheduled for:
NA Datacenter: Saturday, Jan 21st, 12:00 AM ET – 05:00 AM ET
EU Datacenter: Friday, Jan 20th, 6:00 PM ET – 11:00 PM ET