Cannot use a scalar value as an array - Laravel - php

Question

I'm trying to create a function in laravel, but when I send a post request the data is updated successfully but I get cannot use a scalar value as an array error.
Route:
Route::post('transfer-gate-request/{id}',[GateRequestController::class,'transferRequest']);
Request: POST: http://127.0.0.1:8000/api/transfer-gate-request/333
if I switch to PUT route & request, I get Undefined array key "gate_department_id" error
// Transfer Requests
public function transferRequest(Request $request, $id)
{
$user = Auth::user();
if ($user->role_id == 4 || $user->role_id == 3) {
$postData = $request->all();
$gate_department=GateDepartment::where('id', $postData['gate_department_id'])->first();
$data = GateRequest::where('id',$id)->update([
'gate_department_id' => $postData['gate_department_id'],
'department' => $gate_department->name,
'waiting_of_approval' => $gate_department->first_approver_id,
'approved_first' => null,
'approved_second' => null,
'approved_third' => null,
'first_approve_time' => null,
'second_approve_time' => null,
'third_approve_time' => null,
'approve_counter' => 0,
]);
$data['status'] = 1;
$data['message'] = 'Gate request transferred successfully!';
return response()->json($data);
} else {
$data['gate_request'] = null;
$data['message'] = 'You are not authroized to check gate requests';
$data['status'] = 1;
return response()->json($data);
}
}