How can I add service call in SAP B1 SDK?

问题

I want to add service call in SAP B1 SDK but I'm getting the following error message

Notice: Trying to get property of non-object in C:\wamp

Error:-5002

Below are sample codes of PHP

$oService=$mycomp->GetBusinessObject(191);
$oService->CallType=5;
$oService->CustomerCode="460201";
$oService->subject="Text here";

$oService->Add;

Is there any other field which is mandatory

来源：https://stackoverflow.com/questions/57376155/how-can-i-add-service-call-in-sap-b1-sdk