More than likely you are seeing this because the device's ESN is not in Sprint's database or for some reason usually due to long inactivity it has been removed. If this is the case then the ESN will need to be added into the system by an agent creating a "ticket". This process can take up to 3 days to take care of depending on what information is left out etc.
Sprint S.M.A.R.T Agents Sprint S.M.A.R.T Agent are here to help Monday through Sunday 6:00 AM CT - 10:00 PM CT. If you need to speak to an agent outside of these hours, please visit Sprint Chat