the lookup reference could not be resolved

I have two entities Province and Districts

I have these fields in province table

1-Province Code

2-Province Name

and In my province table I have 1,2,3,4,5,6,7,8 provinces data

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Now My district table have these columns

Name,District_code,Province_Code(LookUp from province table) and when I am importing data it get failed by giving this error message "the lookup reference could not be resolved" Although I cross verify all the province code which i am importing from excel is available in master province table but district data is not getting imported.