When you add or invite sub users, make sure to assign a device to that user.
STEP 1. Click on Devices on the sidebar, locate the specific device you want to assign to user and click the Blue Pencil Icon to Edit.
STEP 2. Click the 'Assigned To' and select the users email address. Click Save.
To assign a device to a new sub-user: Survey Kiosk Module -> Device & User -> Devices -> Edit -> Assign to: input your sub-users name