So, it’s not possible to import a lot of lines with a value “1” ? The funny thing, that when I create a few customers manually and export them - no problems, there are the same values for key 3.
Duplicate entry ‘1’ for key 3 does not means the duplicate parameter is the key 3, but means the duplicate is somewhere between key 1 and 3.
For a customer, it is probably the key 1, so the name of customer that alreay exists.