This guide explains how to pair Calendly with Achieve so that all bookings made or update via Calendly automatically appear in Achieve under the Appointments section.
Navigate to https://app.achieveiec.com/integrations
Click on Connect to the right of Acuity.

Put in the email address & password attached to your Calendly account. It does not have to be the same email attached to your Achieve account. Then press Allow Access.
If you use the free version of Calendly, you'll see an error on the Integration page. That is because, based on the webhook's rules, the free version is not meant to work with Achieve. However, the meetings actually do show up in Achieve for free Calendly users, too. You can absolutely ignore that error!
Once the integration is complete, you & your student will automatically begin seeing all appointments made via Calendly in the Appointments section of Achieve.

Meetings sync between Achieve & Calendly using email addresses. If a meeting isn't showing up in Achieve, make sure the student used the email attached to their Achieve account when booking the meeting!
Done 🚀