After selecting the products to be sold, proceed to your shopping cart by clicking the green button at the bottom of the screen.
Notice an ellipsis (...) located at the lower portion of the screen. Press that button.
The first option is "Add Observation."Press it.
Type in the observation.
Hit "Save" at the bottom of the screen.
The observation is shown in blue right below the sales total.
Press the green button to proceed.
That's it! Now all you have to do is complete the sale!