I upgraded the hardware from sync 1 to sync 3.4, everything work well, except missing ESN number.
I tried to download may firmware version from Cyanlabs from 3.3 to 3.4 and updated it, but all are still same, nothing appear on ESN number.
Can someone advise me the reasons and how to fix it 
Did you perform a master reset after install?
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This, its well known ESN won’t show sometimes if you don’t master reset
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I did master reset once done the installation.
Also tried with many version of sync 3.4 and now is running 3.3
All are same result, still had no ESN 
Was there an ESN and part number on the external tag on the unit?
Run the APIM Interrogator Utility to see the ESN and other info for the unit.
Let me tried,
Thanks so much
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