[BUG] addClient API returns empty response (v2.6.0)

[keeldj]

Describe the bug

Hello,

I'm experiencing an issue with the addClient API endpoint in 3x-ui v2.6.0.

Problem:
When attempting to add a client to an inbound via the /panel/inbound/addClient API endpoint, the server returns an empty string ("") as a response, instead of a JSON object (either success or error JSON).

Expected behavior:
The API should return a valid JSON response, indicating either successful client addition or an error message in JSON format.

How to repeat the problem?

Steps to reproduce:

1. Access the 3x-ui panel via API (e.g., login).
2. Send a POST request to /panel/inbound/addClient with a valid session token and a client configuration in the request body (as shown in "Request Body" below).
3. Observe the response.

My setup:

• 3x-ui Version: v2.6.0 (latest stable release from GitHub releases page)
• Xray-core Version: 25.5.16 (from XUI logs)
• Operating System: [Ubuntu 22.04 LTS]
• Installation Method: bash <(curl -Ls https://raw.githubusercontent.com/MHSanaei/3x-ui/main/install.sh) (which currently installs v2.6.0)

Request Method: POST
Request URL Example: http://193.23.210.34:7030/IafRxicsn9yqpDN/panel/inbound/addClient
Request Headers:

• Cookie: _xui_session=<session_token_obtained_from_login>
• Content-Type: application/json

Request Body (example from bot logs):

{
   "id": "inbound-53459",
   "settings": {
      "clients": [
         {
            "id": "6309b9e8-cfc9-42f8-9957-c214704bdd1d",
            "flow": "",
            "email": "user_301404806_3_month",
            "limitIp": 0,
            "totalGB": 0,
            "expiryTime": 0,
            "enable": true,
            "tgId": "",
            "subId": "hbwj7dcw19gh66dkobpm",
            "comment": "",
            "reset": 0
         }
      ]
   }
}



Observed Response:

An empty string ("") is returned.
HTTP Status Code: Unknown, as no JSON response is provided, and no specific HTTP status code is logged by the bot.
Important: No errors related to this API call are logged in the 3x-ui journalctl -u x-ui logs when this happens.
Additional Information:

Logging into the 3x-ui panel via API (/login) works successfully and returns a valid session token.
Manually adding clients via the 3x-ui web interface works without any issues.
Disk space and inode usage on the server are healthy.
I noticed a potentially related issue: https://github.com/MHSanaei/3x-ui/issues/2888, where another user reported issues with addClient API from a bot, although with a different error message (Received HTTP/0.9 when not allowed). This suggests a broader problem with addClient API interactions.
This issue prevents automated client management via API. Any guidance or fix would be greatly appreciated.

Thank you.

### Expected action

The `addClient` API should return a JSON response (either success or an error message in JSON format) after successfully adding a client or encountering an issue.

### Received action

The `addClient` API returns an empty string ("") as a response. No JSON is returned.

### 3x-ui Version

v2.6.0

### Xray-core Version

25.5.16

### Checklist

- [x] This bug report is written entirely in English.
- [x] This bug report is new and no one has reported it before me.

[kaivdev]

I think the problem may be that you write id": "inbound-53459 in the id field, try writing just "id": 53459, although the number is too large for id.