APNs Background Push Success but Wallet Pass Fails with ‘Unable to Deserialize JSON Payload’ on Device

I'm working on implementing Apple Wallet passes using background push notifications.

My server successfully sends the push notification using APNs. The response from the server is HTTP/2 200, and the device receives the push — I can confirm this from device logs.

However, the device logs show the following error: "Failed to parse JSON message payload for topic <private>" "Unable to deserialize JSON message payload"

My payload is below 2 payload. //string payload = "{"aps":{"content-available":1}}"; string payload = JsonConvert.SerializeObject(new { aps = new Dictionary<string, object> { { "content-available", 1 } } });

                    string curlArgs = $"-s -o nul -w \"%{{http_code}}\" " +
                                      $"--data-binary \"{payload}\" " + 
                                      $"-H \"apns-topic: {bundleId}\" " +
                                      $"-H \"apns-push-type: background\" " +
                                      $"-H \"apns-priority: 5\" " +
                                      $"-H \"content-type: application/json\" " +
                                      $"-H \"authorization: bearer {jwt}\" " +
                                      $"--http2 https://api.push.apple.com/3/device/{token}";

I’ve confirmed that:

The device has the Wallet pass installed.

The apns-topic header is set to my passTypeIdentifier.

The apns-push-type is background and apns-priority is 5.

Steps to Reproduce: Install Wallet pass on iOS device.

Send background push to device using the above payload.

Observe the device logs using Console.app or log stream.

See error: unable to deserialize JSON message payload.

Is there a specific payload format expected for Wallet passes? Or any additional fields required in the push payload to avoid this deserialization error?