FASTag users receive their Customer ID along with their FASTag sticker. To get the customer ID, users can check the welcome email sent to their registered email address. The email contains a 13-digit customer ID, starting with the number 17. You will also get your customer ID via SMS (from your FASTag issuing bank) on your mobile number. Another quick and hassle-free manner to get your Customer ID is by using your mobile number. From your registered mobile number (used at the time of purchasing FASTag), call the toll-free number of your FASTag issuing bank to know your customer ID.