Overview
If you are concerned about un-invited attendees joining your meeting, Amazon Chime provides the ability for organizers or their delegates to Lock their meetings.
When you lock a meeting, users who have not been invited and try to join will receive a message that the meeting is locked and they are not connected.
Note: Attendees who are listed on the roster are considered invited and may return to a meeting that is locked if they drop or leave.
Note: If there are attendees listed on the roster that you do not want to be able to join after the meeting is locked, the host may also use the Windows or macOS desktop client to click on the attendee name in the roster and choose Remove from meeting.
Dial-in users who are prevented from joining will hear a voice cue that the meeting is locked. Users attempting the other forms of joining above will receive a message that the meeting is locked - similar to the one below:
How can attendees connect using dial-in or an in-room video conference system once the meeting is locked?
When a meeting starts, Amazon Chime generates a special 13 digit unique PIN for each user invited to a meeting. When a user using an Amazon Chime app joins the meeting the 13 digit unique PIN is displayed (and in some cases entered by the app) by choosing the Dial-in option or Switch to Dial-in.
Please note that each unique 13 digit PIN can only be used by one attendee.
Can I add attendees to a Locked meeting?
Yes, you can choose More > Invite Others and select user(s) from your Contacts and they will be able to join. Also, if you know someone is trying to join that is being locked out. You can quickly unlock the meeting, wait for them to join and then lock the meeting again.
How do I Lock and Unlock my meeting?
During a meeting, the organizer or their delegate(s) can choose More > Lock Meeting or select the 
icon in the Call controls. A dialog is displayed describing the resulting experience.
Choose Lock to proceed.
The Meeting Information will display Meeting Locked when the meeting is locked and the Meeting ID when the meeting is Unlocked.
To unlock your meeting, the organizer or their delegate(s) chooses More > Unlock Meeting or toggles the icon in the Call controls. A dialog is displayed describing the resulting experience.
Choose Unlock to proceed.