Square API - invalid character 'C' looking for beginning of value - php

Question

I am using Square Charge API, and following is my request object for a test card -
I am using Square provided PHP client to connect to the API. And I am receiving following response for "Charge" endpoint -
[HTTP/1.1 400 Bad Request] {"errors":[{"category":"INVALID_REQUEST_ERROR","code":"BAD_REQUEST","detail":"invalid character 'C' looking for beginning of value (line 1, character 1)"}]}
Following is my code in PHP -
public function chargeCustomerCard($userId, $custId, $cardId, $note, $billingAddres, $amount, $idempotencyKey){
$billingAddrRequest = array("address_line_1" => $billingAddres->addr1, "address_line_2" => $billingAddres->addr2, "locality" => $billingAddres->city, "administrative_district_level_1" => $billingAddres->state, "postal_code" => $billingAddres->zip, "country" => $billingAddres->country);
$billingAddressReq = new \SquareConnect\Model\Address($billingAddrRequest);
$moneyRequest = array("amount" => $amount, "currency" => "USD");
$money = new \SquareConnect\Model\Money($moneyRequest);
$request = array("idempotency_key" => $idempotencyKey, "customer_id" => $custId, "customer_card_id" => $cardId, "delay_capture" => false, "amount_money" => $money, "billing_address" => $billingAddressReq, "note" => $note, "reference_id" => $userId);
$charge = new \SquareConnect\Model\ChargeRequest($request);
$response = null;
try{
$charge_api = new \SquareConnect\Api\TransactionsApi();
$response = $charge_api->charge($this->authtoken, $this->locationId, $charge);
if($response != null && count($response->getErrors()) == 0){
$transaction = $response->getTransaction();
$data = array();
$data['transactionId'] = $transaction->getId();
$data['created'] = $transaction->getCreatedAt();
$data['referenceId'] = $transaction->getReferenceId(); //this should be equal to userid
$tender = $transaction->getTenders()[0];
$data['tenderId'] = $tender->getId();
$data['note'] = $tender->getNote();
$data['amount'] = ($tender->getAmountMoney()->getAmount())/100;
$data['currency'] = $tender->getAmountMoney()->getCurrency();
$processingFee = $tender->getProcessingFeeMoney();
if(isset($processingFee) && !empty($processingFee)){
$data['processingFee'] = $tender->getProcessingFeeMoney()->getAmount();
}else{
$data['processingFee'] = 0;
}
$data['tendertype'] = $tender->getType();
$data['cardStatus'] = $tender->getCardDetails()->getStatus();
$data['cardBrand'] = $tender->getCardDetails()->getCard()->getCardBrand();
$data['cardLast4'] = $tender->getCardDetails()->getCard()->getLast4();
$data['idempotencyKey'] = $idempotencyKey;
$data['customerPayId'] = $custId;
$data['customerCardId'] = $cardId;
return $this->generateReturnData(PAY_API_SUCCESS, '', $data);
}else{
return $this->generateReturnData(PAY_API_FAIL, '', $response->getErrors());
}
}catch(Exception $e) {
return $e->getMessage();
}
}
Can someone please point out to me what am I doing wrong here. I am really stuck here. Other API endpoints are working fine, such as, Create Customer, Create Customer Card API endpoints, using the same approach and same PHP client provided by square.
PS - this is on sandbox