At the bottom of the HUB message screen, you will find a dropdown menu. See brown box and arrow in image below.
Here it is close up:
If you click on the downward arrow, the following box will pop up:
Note that at the moment, the Short code button is toggled on (purple color in image above). Simply click on the Toll-free number button to toggle it on (brown circle above).
The Toll-free number button will toggle on (purple color) and the Short code button will automatically be toggled off (greyed out color).
Then, click on Close and continue writing, scheduling, or sending your message like normal.
Keep up to date with changes to short codes via this article on our website: