Bulk Import API Fail

Hello,
We are consuming the bulk import api and after testing in code as well as in post man, only the first column of the csv file sent is getting updated in the list we specified. I really don't know why. If we upload the list manually from Marketo New > Import List, it works.

Endpoint: /bulk/v1/leads.json?access_token={access_token}&format=csv&listId={listId}