To add a Sub-Contractors cost to a "Job / New Call-Out" you need to create an order to the Sub-Contractor. The cost would then be added as a miscellaneous item and the order received to an existing "Job / Call-Out". This would then reflect on the invoice to the client.
1. Navigate to Inventory → Orders.
2. Click on the (+) to add an Order.
3. Select the Cost To.
4. Select the Job / Call-Out.
5. Select the Sub-Contractor from the Supplier drop down.