To get a good overview of your participants and their check-in codes it's always a good idea to create a list to keep track of things.
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1. Create a Dynamic List of Participants

2. In the Fields tab, make sure to select Check-in code 

3. In the Check-in tab, you can select to add Check-in Points to your list. You can also select whether to display a Check mark, First check in time or Number of check-ins.

4. In the example list below, you are able to view which participants have been assigned a custom check-in code. (1001, 1002, 1003, 1004, 1005, 1006). You are also able to view the date and time of their Check-in.