The Please Remeasure White error is received when attempting to calibrate the device.
First time users typically receive the error if the cover has not been removed from the calibration module within the kit. You'll want to be sure to pop/twist the cap off before calibrating the device. The white puck should be pressed flushed up against the glass screen of the device. Please see the links below on how to calibrate the Purpl Pro.
If you've calibrated successfully and still receiving the error, check the condition of the white puck. If it does become dirty or skewed it can effect the calibration step. If un-sure of the condition, feel free to snap a photo of the white puck and send it for review by creating a ticket. Replacements can be purchased at getpurpl.com. It's advised to swap out calibration modules yearly.
If the condition of the white puck appears to be good, you can also check the status of the firmware if an older device to see if up to date or not to v 0.16.0. Please see the article on how to check your firmware. https://purplscientific.freshdesk.com/a/solutions/articles/64000263077
If the calibration module is in good condition and the firmware is up to date, then it may be potential hardware failure. If that's the case, then a Service Repair or RMA will be initiated.