Iphone HEX DEX

trying activate iphone 4 bought used. upon online activation, asks serial number. enter serial number , not correct format.
told me find hex or dex number guess, identifer (udid).
through itunes found udid, 40 digit number. same serial 11 digit number found on iphone itself, through settings..general..about?

 

14 digit meid#

 

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