There must always be a listing before making a sale.
When entering in a Sale (or Listing) you have the option to "Count As" as a full sale, half sale, or do not count.
*These only reflect in your target NUMBERS, not commission $ or % figure.
(i.e if you select "Half a Listing" your monthly property number would now be 0.5)
Now you can add a sale, as usual, using the "+" on the homepage. The new listing will appear in the drop-down menu to select from. If the commission is also being split or is $ amount versus %, refer to this article - Adding Commission % versus $.