Dynamically-created Twilio Enqueue waitUrl results in 500 server error - php

Question

I have a function in my Laravel application that generates TwiML for a holding queue. It seems that when I try to dynamically generate the value for the waitUrl attribute, I end up getting a 500 server error during runtime. Routes are properly established and I'm able to view the correct XML at the waitURL in the browser. However, the error persists.
If I create a static XML file with the same exact content, or use a TwiML Bin, it works like a charm.
Here are the relevant functions:
public function wait() {
return $this->generateWaitTwiml();
}
public function onHold($agentId) {
return $this->generateHoldQueueTwiml($agentId, '/phone/wait');
}
private function generateHoldQueueTwiml($agentId, $waitUrl = null) {
$queue = $agentId . '_hold';
if ($waitUrl === null){
$waitUrl = 'path_to_static.xml';
}
$queue = $agentId . '_hold';
$response = new Twiml();
$response->enqueue(
$queue,
['waitUrl' => $waitUrl]
);
return response($response)->header('Content-Type', 'application/xml');
}
private function generateWaitTwiml() {
$response = new Twiml();
$response
->play('http://path_to_my.mp3');
return response($response)->header('Content-Type', 'application/xml');
}

Answer 1

This was resolved by excluding the URIs from the CSRF verification (in VerifyCsrfToken.php):
class VerifyCsrfToken extends Middleware {
protected $except = [
'uri/',
'uri2/*',
];
}