In order to send messages using CSV file, your .csv file should indeed include 2 fields:

1. Phone number - in an international format.

2. Your message.

You can import a .csv file:

Make sure your cell is configured as a number with 0 decimal places:

Then you would need to create a custom field (in this example, a field called ‘message’):

When importing a list, map the relevant fields so the mobile number is your phone field
then scroll all the way down and point your message to the text within your .csv file.

It will look like this:

In the message editor, click on the ‘message’ tag (or any other name of your choice):

The outcome: