You can now enter the sales commission amount for an Opportunity in the Sales app, as a flat fee.
You can specify either a flat fee, or a %, or both. In the Sales Commission section in the Sales web app, the commssion is calculated as the sum of the flat fee and the % of the opportunity amount, if specified.
On the mobile, you can only view the commission figures, and not edit them. On the web, only admins and managers can edit the commissions.