A job's capacity setting is also turned on when route optimisation is enabled. This feature allows you to set a capacity allowed for a vehicle and a capacity required on a job. The vWork optimisation module will then prevent overloading a vehicle.
Capacity can be measured however you like: meals, boxes, pallets, tonnes, cubic metres, etc. But you need to use the same metric on both vehicles and jobs. You cannot use capacity to solve complex load planning problems.
For example, a small van could carry 100 meals, and a customer may order two meals in a job.
You would then need to add a capacity of "2" to a job, so include the following XML in a PUT or a POST to the job in question:
<required_capacity>2</required_capacity>