While import is completed, you can check the Import history tab and see if there are any errors.

If yes, you will see two file links:

Error Report file will show the information on why the line got error. You can use this messages to fix the issues with those lines.

Failed Records file will show you the lines themselves. You can use that file for fixing the lines and also import after fixing as the file will have the same structure as the correct import template.

The line sequence in both files correspond to each other so the first error information is about the first line in the failed records file.