Problem with json_decode - Syntax error, malformed JSON

I'm receiving a json array from php as the return of curl_exec in PHP (first json PHP -> python, that returns another json), and decode fails due to bad syntax.

The piece of API code:

if($_GET['url'] == 'tomorrowdate'){
    $tomorrow = date('Y-m-d', strtotime(' + 1 days'));
    $risposta = [
        "tomorrow" => $tomorrow
    ];
    echo json_encode($risposta);
    http_response_code(200);
}

the curl code:

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_HEADER, array('Content-type: application/json'));
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
$output = curl_exec($ch);
//var_dump($output);
$data = stripslashes($data);
$json_array = json_decode($output, true);

//var_dump(curl_error($ch));

curl_close($ch);

var_dump($json_array);

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;
    }

I tried to adapt your code with mine but the problem remains ...

function remove_utf8_bom($text){
    $bom = pack('H*','EFBBBF');
    $text = preg_replace("/^$bom/", '', $text);
    return $text;
}
$tomorrow = date('Y-m-d', strtotime(' + 1 days'));
$risposta = [
            "tomorrow" => $tomorrow
           ];
$json = remove_utf8_bom($risposta);
echo json_encode($json);
var_dump(json_decode($json_encode, TRUE));

The output is:

{"tomorrow":"2018-09-15"}NULL - Syntax error, malformed JSON

Copyright Notice：Content Author:「Manu Blackwell」，Reproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/52337698/problem-with-json-decode-syntax-error-malformed-json