We often get emails from users having trouble uploading a .csv. There are a few things to check on your .csv that may be causing the issues:
The first thing to do is to check that all users have an email address. If there are users without email addresses the upload will not work. Also check emails are correct have .com .co.uk .org etc.
Next check if there are any duplicates. If a user is featured more than once the upload will not work, as a user can only be uploaded once per file.
Remove any headings. The .csv will not upload if there are any rows/columns without an email address in it, so remove the headings for it to work.
If you continue to have trouble uploading your .csv after following the steps above, please contact firstname.lastname@example.org.