When you try to import your subscribers from a text or csv file, sometimes you might get an error like:
Your form has a few errors, please fix them and try again! The file "filename.csv" cannot be uploaded. Only files of these MIME-types are allowed: text/comma-separated-values, text/csv, application/csv, application/excel, application/vnd.ms-excel, application/vnd.msexcel, text/anytext, text/plain.
This happens because the file you try to upload does not have the correct mime type, i.e: you upload a csv file but it is identified as a text file and it’s not allowed.
In order to fix this problem, you can go to Backend > Settings > Import/Export and set “Check mime type” to No, then try uploading the file again, this time it will work.