Paypal IPN总是返回INVALID - php

Question

I've tried multiple different examples of IPN classes and every time paypal returns with INVALID in the IPN simulator.

End point: https://ipnpb.sandbox.paypal.com/cgi-bin/webscr

I've done some testing, and the data I'm returning to paypal looks the same. e.g.

What paypal is sending:

payment_type=echeck&payment_date=Sun%20Jun%2010%202018%2010%3A17%3A15%20GMT%2B0100%20%28GMT%20Summer%20Time%29&payment_status=Completed&address_status=confirmed&payer_status=verified&first_name=John&last_name=Smith&payer_email=[e-mail]&payer_id=TESTBUYERID01&address_name=John%20Smith&address_country=United%20States&address_country_code=US&address_zip=95131&address_state=CA&address_city=San%20Jose&address_street=123%20any%20street&business=[e-mail]&receiver_email=[e-mail]&receiver_id=[e-mail]&residence_country=US&item_name=something&item_number=AK-1234&quantity=1&shipping=3.04&tax=2.02&mc_currency=USD&mc_fee=0.44&mc_gross=12.34&mc_gross_1=12.34&txn_type=web_accept&txn_id=300182286&notify_version=2.1&custom=xyz123&invoice=abc1234&test_ipn=1&verify_sign=undefined

What I'm sending Paypal

cmd=_notify-validate&payment_type=echeck&payment_date=Sun%20Jun%2010%202018%2010%3A17%3A15%20GMT%2B0100%20%28GMT%20Summer%20Time%29&payment_status=Completed&address_status=confirmed&payer_status=verified&first_name=John&last_name=Smith&payer_email=[e-mail]&payer_id=TESTBUYERID01&address_name=John%20Smith&address_country=United%20States&address_country_code=US&address_zip=95131&address_state=CA&address_city=San%20Jose&address_street=123%20any%20street&business=[e-mail]&receiver_email=[e-mail]&receiver_id=[e-mail]&residence_country=US&item_name=something&item_number=AK-1234&quantity=1&shipping=3.04&tax=2.02&mc_currency=USD&mc_fee=0.44&mc_gross=12.34&mc_gross_1=12.34&txn_type=web_accept&txn_id=300182286&notify_version=2.1&custom=xyz123&invoice=abc1234&test_ipn=1&verify_sign=undefined

Paypal returned: 'INVALID'

The code I'm currently using is this:

public function verifyIPN()
{
    if ( ! count($_POST)) {
        throw new Exception("Missing POST Data");
    }

    $raw_post_data = file_get_contents('php://input');
    $raw_post_array = explode('&', $raw_post_data);
    $myPost = array();
    foreach ($raw_post_array as $keyval) {
        $keyval = explode('=', $keyval);
        if (count($keyval) == 2) {
            // Since we do not want the plus in the datetime string to be encoded to a space, we manually encode it.
            if ($keyval[0] === 'payment_date') {
                if (substr_count($keyval[1], '+') === 1) {
                    $keyval[1] = str_replace('+', '%2B', $keyval[1]);
                }
            }

            $myPost[$keyval[0]] = urldecode($keyval[1]);
        }
    }

    // Build the body of the verification post request, adding the _notify-validate command.
    $req = 'cmd=_notify-validate';

    if (function_exists('get_magic_quotes_gpc')) {
        $get_magic_quotes_exists = true;
    }

    foreach ($myPost as $key => $value) {

        if ($get_magic_quotes_exists == true && get_magic_quotes_gpc() == 1) {

            $value = rawurlencode(stripslashes($value));
        } else {
            $value = rawurlencode($value);
        }
        // Added this line to see if it helps
        $value = str_replace('%40', '@', $value);
        $req .= "&$key=$value";
    }

    // Post the data back to PayPal, using curl. Throw exceptions if errors occur.
    $ch = curl_init($this->getPaypalUri());
    curl_setopt($ch, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_1_1);
    curl_setopt($ch, CURLOPT_POST, 1);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    curl_setopt($ch, CURLOPT_POSTFIELDS, $req);
    curl_setopt($ch, CURLOPT_SSLVERSION, 6);
    curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 1);
    curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 2);

    // This is often required if the server is missing a global cert bundle, or is using an outdated one.
    if ($this->use_local_certs) {
        curl_setopt($ch, CURLOPT_CAINFO, __DIR__ . "/cert/cacert.pem");
    }

    curl_setopt($ch, CURLOPT_FORBID_REUSE, 1);
    curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 30);
    curl_setopt($ch, CURLOPT_HTTPHEADER, array(
        'User-Agent: PHP-IPN-Verification-Script',
        'Connection: Close',
    ));

    $res = curl_exec($ch);

    if (!($res)) {
        file_put_contents("paypal-errors.txt", "error no: ".$errno($ch)." errorstr: ".curl_error($ch));
        $errno  = curl_errno($ch);
        $errstr = curl_error($ch);
        curl_close($ch);
        throw new Exception("cURL error: [$errno] $errstr");
    }

    $info      = curl_getinfo($ch);
    $http_code = $info['http_code'];

    if ($http_code != 200) {
        file_put_contents("paypal-errors.txt", "error http status response = ".$http_code);
        throw new Exception("PayPal responded with http code $http_code");
    }

    curl_close($ch);
    file_put_contents("paypal-sent.txt", "response: ".file_get_contents('php://input'));
    file_put_contents("paypal-result.txt", "response: ".$res);

    // Check if PayPal verifies the IPN data, and if so, return true.
    if ($res == self::VALID) {
        return true;
    } else {
        return false;
    }
}

So at this point, I'm assuming there is something wrong with my environment. My server has TLS 1.2 and 1.3. I've ran out of ideas for troubleshooting. Any help would be greatly appreciated!