You type "serial number" into the IDnow status check page, and it says "Not found." The Reality: You are entering a phone number or a random number. The status page requires the Transaction ID (usually starting with T- or a 32-character hex string). Solution: Check your email for the subject line "Your identification with IDnow is complete." The Transaction ID is there.
If you are looking for the serial number of the (used for rapid flu or COVID-19 testing), you can locate it in two places: idnow serial number