How do I send data to Appian, to start a process model from third party applicat

it's the process instance ID, not the taskId

The web service returns you a process id. So you can then use this to get a task id to use in your embedded sail form.

I have a Windows application. We are have a CEF Sharp browser, which loads the embedded HTML of the process model. Now, I want this windows application to send the data to this process model. How do I do that?

how can I get task id from process id?

Hi Ishaan,
If you are looking for starting the process in external web pages using embedded interfaces. Kindly refer the below link.
forum.appian.com/.../Embedded_Interfaces.html