Cannot send iOS push notifications - 400 BadDeviceToken response - apple-push-notifications

Question

I have generated the .pem files for development using these commands in the Mac terminal:
openssl x509 -inform der -outform pem -in aps_development.cer -out PushNotificationAppCertificate.pem
openssl pkcs12 -in PushNotification.p12 -out PushNotificationAppKey.pem -nocerts
cat PushNotificationAppCertificate.pem PushNotificationAppKey.pem > PushNotificationAppCertificateKey.pem
And on the server I use PHP:
$curl = curl_init();
$device_token = "oVVEyzOm8LYn1nEYQLUcp1nBQw+UKHUeJbVHxcqr3ls=";
$pem_file = "PushNotificationAppCertificateKey.pem";
$pem_secret = "<password>";
$apns_topic = "<myapp.id>";
$sample_alert = '{"aps":{"alert":"hi","sound":"default"}}';
$url = "https://api.development.push.apple.com/3/device/".urlencode($device_token);
$ch = curl_init($url);
curl_setopt($ch, CURLOPT_PORT, 443);
curl_setopt($ch, CURLOPT_POSTFIELDS, $sample_alert);
curl_setopt($ch, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_2_0);
curl_setopt($ch, CURLOPT_HTTPHEADER, array("apns-topic: $apns_topic"));
curl_setopt($ch, CURLOPT_SSLCERT, $pem_file);
curl_setopt($ch, CURLOPT_SSLCERTPASSWD, $pem_secret);
$response = curl_exec($ch);
$httpcode = curl_getinfo($ch, CURLINFO_HTTP_CODE);
However, BadDeviceToken is the response, and I am not getting the notification on the device.
According to the Apple documentation, either the device token is invalid, or I am using production certificate for the development server or vice versa; neither of which are the case here.
How can I make this work?

Answer 1

I solved it.
The problem was with the device token - if you knew, how they should look like, you would instantly tell it was not acquired the right way. It is not supposed to contain = or + characters, and its length should be 64 characters.
In my RegisteredForRemoteNotifications() function (Xamarin.iOS) I had used the
deviceToken.GetBase64EncodedString(NSDataBase64EncodingOptions.None)
function to get the token in string form. But the correct procedure is
byte[] bytes = deviceToken.ToArray<byte>();
string[] hexArray = bytes.Select(b => b.ToString("x2")).ToArray();
string tokenString = string.Join(string.Empty, hexArray);