Contacts must be assigned to a button before you visitors can select those contacts while checking in. Think of buttons as the doors your visitors can enter, and the contacts assigned to those buttons as the folks your visitors might go through that door to see. You can assign your contacts one by one or en masse.
To assign contacts one at a time, go to the Employee Contacts page and click the pencil icon next to the contact. Below your contact's personal information is the assignment and messaging preference options. Toggling on any button in the "Button Assignment" section will assign contacts to the selected button. Be sure to save!
If you want to mass-assign all or many contacts, navigate to the Buttons page of your dashboard. Select 'Existing Buttons' on the right, then 'edit' for the button you want to assign contacts to. Scroll down to the 'Select Employee Contacts' section. Now you can select all (or check boxes for specific contacts)!