Google API Data Transfer Insert: missing resource.applicationDataTransfer - php

Question

I'm creating simple PHP script for transfering ownerships of drive files between users in the same domain. I want to use Admin SDK Transfers and Insert method.
Google has documentation about transfers here
I tried to transfer data through their webpage GUI and it went fine. What I can't do is how to make it work with PHP Client library.
Let's say I have prepared object for creating requests to Transfers resource
$transfers = new \Google_Service_DataTransfer($googleConnection);
googleConnection handles service account authorization so i can make requests like this:
$data = $this->transfers->transfers->listTransfers();
This returns data of all existing transfers in domain. Based on documentation and PHP Client library insert operation should work also.
$transferParams = new \Google_Service_DataTransfer_ApplicationTransferParam();
$transferParams->setKey("PRIVACY_LEVEL"); //what kind of docs I want to transfer
$transferParams->setValue(['SHARED', 'PRIVATE']);
$appDataTransfer = new \Google_Service_DataTransfer_ApplicationDataTransfer();
$appDataTransfer->setApplicationTransferParams($transferParams);
$appDataTransfer->applicationId = "iDString"; //set application ID
$newTransfer = New \Google_Service_DataTransfer_DataTransfer();
$newTransfer->setOldOwnerUserId('accountID'); //origin account IDs are placeholders
$newTransfer->setNewOwnerUserId('account2ID'); //destination account
$newTransfer->setApplicationDataTransfers($appDataTransfer);
$result = $this->transfers->transfers->insert($newTransfer); //execute insert
After executing insert I am getting code 400 with message Missing required field: [resource.applicationDataTransfer].
If I test real parameters via web they work.
I must be missing something, because that exception doesn't make sense at all.
I'm also open to alternative solutions.

Answer 1

setApplicationDataTransfers method expects an array of Google_Service_DataTransfer_DataTransfer so you just need to update the following line (note the [] in the params)
$newTransfer->setApplicationDataTransfers([$appDataTransfer]);