Automated Workflow Question

I have a sheet where each row holds the details of an event. Each event has a start date, and I've set up automated workflows to send event attendees reminder messages. One flow is set up to send an "initial" reminder message 21 days out from the start date. The other flow is set up to send a "final" reminder message 14 days out from the start date. 

However, attendees are getting both reminders at once. For example, one attendee has an event scheduled to start on 8/17, and she got the 14 day and 21 day out reminders today. I've looked over the automations very carefully and think they are set up correctly but is there something I'm not understanding about workflows to cause this? 

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