In C#, we use Microsoft.VisualStudio.Services.WebApi.Patch.Json.JsonPatchDocument to pack a completed request body Json, then pass it into the method.
See below sample:
var patchDocument = new
Microsoft.VisualStudio.Services.WebApi.Patch.Json.JsonPatchDocument();
patchDocument.Add(new Microsoft.VisualStudio.Services.WebApi.Patch.Json.JsonPatchOperation() {
Operation=Operation.Add,
Path= "/fields/System.WorkItemType",
Value="Task"
});
patchDocument.Add(new Microsoft.VisualStudio.Services.WebApi.Patch.Json.JsonPatchOperation()
{
Operation = Operation.Add,
Path = "/fields/System.State",
Value = "To Do"
});