The “Check sensor” display message might mean that the FreeStyle Libre 3 Plus sensor tip is not under your skin.
Try to start your sensor again. If you continue to see “Check sensor” on the screen, your sensor may not have been applied properly. Remove this sensor and apply and start a new sensor.
If you needed to start a new sensor before the 15 days of wear were complete please visit the quick and convenient online sensor support request form, or contact Customer Care Customer Care which is available at 1-855-632-8658 7 days a week from 8AM to 8PM Eastern Time; excluding holidays.