json write read decode parsing last error

<?php
    if( ! file_exists( '/config/credentials.json' ) ){
      $filename = "/config/credentials.json";
      $fp = fopen($filename, 'w');
      $arr = array();
      $arr[ 'account_sid' ] = $this->expectedAccountSid;
      $arr['api_version'] = $this->expectedApiVersion;
      $arr['auth_token'] = $this->expectedAuthToken;
      $arr[ 'endpoint' ] = $this->expectedEndpoint;

      fwrite($fp, json_encode( $arr , JSON_UNESCAPED_SLASHES));
      fclose($fp);
    }



    $filename = "/tmp/myfile.json";
    $contents = file_get_contents( $filename );
    print $contents . "\n";
    $myvar = json_decode( $contents, true );



$json[] = '{"Organization": "PHP Documentation Team"}';

// An invalid json string which will cause an syntax error, in this case we used ' instead of " for quotation
$json[] = "{'Organization': 'PHP Documentation Team'}";


foreach ($json as $string) {
    echo 'Decoding: ' . $string;
    json_decode($string);

    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;
    }

    echo PHP_EOL;
}