If you are having trouble uploading a contact file to MXT, there are a number of things that may be causing this error.
Confirm that the file you are attempting to upload is saved in the correct format. It must be either a CSV or an XLS file (XLSX is not a supported format for uploading).
Make sure there are no spaces or special symbols within the mobile phone numbers.
Try logging out and then logging back in again.
Refer to the following articles on steps to format and upload your files
If you have reviewed the above and you're still experiencing issues, contact our support team below.
Note: Please ensure that you attach the file that you're trying to upload to the ticket.