Stripe Q64.“No signatures found matching the expected signature for payload”.$ expectedSignature is not included in $ signatures

The code where the error occurs.
webhook.php

\Stripe\Stripe::setApiKey('xxxx');

$endpoint_secret = 'whsec_xxxx';

$payload = @file_get_contents('php://input');

$sig_header = $_SERVER['HTTP_STRIPE_SIGNATURE'];

$event = null;

try {

  $event = \Stripe\Webhook::constructEvent(

      $payload, $sig_header, $endpoint_secret

  );

} catch(\UnexpectedValueException $e) {

    http_response_code(400);

    exit();

} catch(\Stripe\Error\SignatureVerification $e) {

    //An error is caught here

}

error message
No signatures found matching the expected signature for payload

▼stripe-php/lib/WebhookSignature.php

$signatureFound = false;

foreach ($signatures as $signature) {

    if (Util\Util::secureCompare($expectedSignature, $signature)) {

        $signatureFound = true;

        break;

    }

}

if (!$signatureFound) {

    throw new Error\SignatureVerification(

        "No signatures found matching the expected signature for payload",

        $header,

        $payload

    );

Results of debugging
$ expectedSignature is not included in $ signatures

'-----signatures-----'

array (

  0 => '171abxxxx',

)

'-----expectedSignature-----'

'd1a55xxxx'