Hi Martial,

You cannot use external IDs to import data between two separate databases. Especially with version changes. Try to export main data points such as name, address, mobile, website and try to  match with version 13 contact export file template.

It seems you have individual contact related to contact of company and when you import these individual contact which related company you will get the external id error So I suggest to get the contacts with Is_company equal true in separate CSV and then get the individual contacts in another CSV file, After that import the first CSV of companies and then import the individual file.

Thanks for your helps , I solved the issue using  all  your  differents  suggestions.