Thanks Shyam!
Looking at the logs, it looks like we had a blip in the Sandbox environment this morning that caused transfers to fail due to no services being available to receive the request.
The services are back up again and I am able to create transfers in my Sandbox test account. Would you be able to try creating transfers again?
As an aside, you should be able to catch the error and get the JSON response-body for errors. You can try wrapping the request in a try/catch and display the error response by calling the getResponseBody() method.
Example:
try{
$new_customer = $customersApi->create([
//request_body
]);
} catch (Exception $e) {
echo 'Caught exception: ', $e->getResponseBody(), "\n";
}
Let me know if you run into any issues!