PHP - JSON Response - cannot remove certain unseen character - 

Question

I have a json response coming back from a webservice, which, to the naked eye is:

{ "fault": { "code" : "Application Error", "message" : "Generic Error Message" } }

However it fails to json_decode - json_decode returns null.

Debugging json_decode with:

 json_decode($response);

    switch (json_last_error()) {
        case JSON_ERROR_NONE:
            echo ' - No errors';
        break;
        case JSON_ERROR_DEPTH:
            echo ' - Maximum stack depth exceeded';
        break;
        case JSON_ERROR_STATE_MISMATCH:
            echo ' - Underflow or the modes mismatch';
        break;
        case JSON_ERROR_CTRL_CHAR:
            echo ' - Unexpected control character found';
        break;
        case JSON_ERROR_SYNTAX:
            echo ' - Syntax error, malformed JSON';
        break;
        case JSON_ERROR_UTF8:
            echo ' - Malformed UTF-8 characters, possibly incorrectly encoded';
        break;
        default:
            echo ' - Unknown error';
        break;
    }

returns the error: Syntax error, malformed JSON

Using my browser console, I can see the actual json string is:

 { "fault": { "code" : "Application Error", "message" : "Generic Error Message" } }

Note the extra  at the start.

I have tried everything to remove this unseen character, but I cannot get rid of it!

e.g.

function cleanString($val)
{
    $non_displayables = array(
    '/%0[0-8bcef]/',            # url encoded 00-08, 11, 12, 14, 15
    '/%1[0-9a-f]/',             # url encoded 16-31
    '/[\x00-\x08]/',            # 00-08
    '/\x0b/',                   # 11
    '/\x0c/',                   # 12
    '/[\x0e-\x1f]/',            # 14-31
    '/x7F/' ,                    # 127
    '//'                     # 127
    );
    foreach ($non_displayables as $regex)
    {
        $val = preg_replace($regex,'',$val);
    }
    $search  = array("\0","\r","\x1a","\t");
    return trim(str_replace($search,'',$val));
}

plus tried using things like stripslashes, html_entity_decode etc

I tested a simple:

$string = str_replace("FEFF","",$string);

and it doesn't remove the FEFF element at all.

My headers are UTF-8.

If I try exactly the same request in Postman (the api tester tool), it works - Postman manages to decode the JSON and display it nicely.

So, somewhere along the line either Postman successfully removes this character, or I am adding it.

Below is the full CURL (PHP) request I am calling, whcih is exactly the same as the PHP Curl code outputted from the Postman call which works:

 $curl = curl_init();
    curl_setopt_array($curl, array(
        CURLOPT_URL => 'https://example.com/?reference=Test',
        CURLOPT_RETURNTRANSFER => true,
        CURLOPT_ENCODING => '',
        CURLOPT_MAXREDIRS => 10,
        CURLOPT_TIMEOUT => 0,
        CURLOPT_FOLLOWLOCATION => true,
        CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
        CURLOPT_CUSTOMREQUEST => 'POST',
        CURLOPT_POSTFIELDS =>'example',
        CURLOPT_HTTPHEADER => array(
          'Accept: Application/json',
          'Subscription-Key: redacted',
          'SOAPAction: example',
          'Content-Type: text/plain',
          'Cookie: Cookiesession=redacted'
        ),
      ));
      
      $response = curl_exec($curl);

I have also tried the same call using GuzzleHTTP and I get the same issue.

How can I get rid of this character, and get the json to validate?

Thanks