It so happens that the service has been performed by a subcontractor and you need a self-cost for those works.

`To add this service tho the ticket you need to:

1. Open the service's card in the ticket.
2. Find the self-cos field.
3. Define the amount paid to the subcontractor.
4. Save the changes.

The self-cost could also be defined by default. You could define it in Settings > Handbooks > Services. It would be used each time the services are being added to the ticket (you can change them after adding) or after the service has been sold via a POS.

It is important to remember that the self-cost is being taken into account while peforming the net profit calculation. The staff is getting the commission based on the net profit.
It so happens that the service has been performed by a subcontractor and you need a self-cost for those works.