SF2400 - Enable MQTT not working: Invalid content length

[ehrenchris]

Hi,

I'm trying to activate local MQTT on my SolarFlow 2400 AC based on your description:

curl --location '192.168.178.192/rpc' \
--header 'Content-Type: application/json' \
--data '{"sn": "HOA1xxxxxxxxx","method": "HA.Mqtt.SetConfig","params": {"config": {"enable": true,"server": "192.168.178.99","port": 1883,"protocol": "mqtt","username": "myuser","password": "mypassword"}}}'

My Json body in pretty:

{
    "sn": "HOA1xxxxxxxxx",
    "method": "HA.Mqtt.SetConfig",
    "params": {
        "config": {
            "enable": true,
            "server": "192.168.178.99",
            "port": 1883,
            "protocol": "mqtt",
            "username": "myuser",
            "password": "mypassword"
        }
    }
}

The majority of the time, I'm just getting an Error (Connection Reset).
Shortly after retrieving the MQTT config (via curl --location '192.168.178.192/rpc?method=HA.Mqtt.GetConfig') I'm able to get a response from the POST request above.

The response is:

HTTP Code 400
Body:
{
    "timestamp": 1758019933,
    "messageId": 19,
    "error": "Invalid content length, The maximum request length is 256",
    "code": 400
}

How can I enable local MQTT?

Firmware of the device is V1.0.6

[dav1dBoy]

Hi,

I'm trying to activate local MQTT on my SolarFlow 2400 AC based on your description:

curl --location '192.168.178.192/rpc' \
--header 'Content-Type: application/json' \
--data '{"sn": "HOA1xxxxxxxxx","method": "HA.Mqtt.SetConfig","params": {"config": {"enable": true,"server": "192.168.178.99","port": 1883,"protocol": "mqtt","username": "myuser","password": "mypassword"}}}'

My Json body in pretty:

{
    "sn": "HOA1xxxxxxxxx",
    "method": "HA.Mqtt.SetConfig",
    "params": {
        "config": {
            "enable": true,
            "server": "192.168.178.99",
            "port": 1883,
            "protocol": "mqtt",
            "username": "myuser",
            "password": "mypassword"
        }
    }
}

The majority of the time, I'm just getting an Error (Connection Reset). Shortly after retrieving the MQTT config (via curl --location '192.168.178.192/rpc?method=HA.Mqtt.GetConfig') I'm able to get a response from the POST request above.

The response is:

HTTP Code 400
Body:
{
    "timestamp": 1758019933,
    "messageId": 19,
    "error": "Invalid content length, The maximum request length is 256",
    "code": 400
}

How can I enable local MQTT?

Firmware of the device is V1.0.6

Thank you for your feedback. I'll increase the length to 512 in a future version.
Currently, can you write it in two steps? For example:
First:
{
"sn": "HOA1xxxxxxxxx",
"method": "HA.Mqtt.SetConfig",
"params": {
"config": {
"enable": true,
"server": "192.168.178.99",
"port": 1883,
"protocol": "mqtt"
}
}
}
Second:
{
"sn": "HOA1xxxxxxxxx",
"method": "HA.Mqtt.SetConfig",
"params": {
"config": {
"username": "myuser",
"password": "mypassword"
}
}
}

[ehrenchris]

Hi @dav1dBoy - Thanks for your reply.

I tried it with your suggestion, but the request is still failing with the same error message:

curl --location '192.168.178.192/rpc' \
--header 'Content-Type: application/json' \
--data '{"sn": "HOA1xxxxxxxxx","method": "HA.Mqtt.SetConfig","params": {"config": {"enable": true,"server": "192.168.178.99","port": 1883,"protocol": "mqtt"}}}'

Response:

{"timestamp":1759213170,"messageId":1,"error":"Invalid content length, The maximum request length is 256","code":400}

Do you have any other suggestion/ idea?

[maxclaudi]

Hi,

I'm trying to activate local MQTT on my SolarFlow 2400 AC based on your description:

curl --location '192.168.178.192/rpc' \
--header 'Content-Type: application/json' \
--data '{"sn": "HOA1xxxxxxxxx","method": "HA.Mqtt.SetConfig","params": {"config": {"enable": true,"server": "192.168.178.99","port": 1883,"protocol": "mqtt","username": "myuser","password": "mypassword"}}}'

My Json body in pretty:

{
    "sn": "HOA1xxxxxxxxx",
    "method": "HA.Mqtt.SetConfig",
    "params": {
        "config": {
            "enable": true,
            "server": "192.168.178.99",
            "port": 1883,
            "protocol": "mqtt",
            "username": "myuser",
            "password": "mypassword"
        }
    }
}

The majority of the time, I'm just getting an Error (Connection Reset). Shortly after retrieving the MQTT config (via curl --location '192.168.178.192/rpc?method=HA.Mqtt.GetConfig') I'm able to get a response from the POST request above.

The response is:

HTTP Code 400
Body:
{
    "timestamp": 1758019933,
    "messageId": 19,
    "error": "Invalid content length, The maximum request length is 256",
    "code": 400
}

How can I enable local MQTT?

Firmware of the device is V1.0.6

---

The device only accepts JSON bodies up to 256 characters.
If curl increases the body size due to incorrect quoting or redirect handling, the device rejects the request.

Solution:
Omit --location
On Windows, it's better to use double quotes " and escape the body with ^ if necessary
Ensure that --data-raw or -d sends exactly the JSON without additional formatting

---

Here are 2 versions for Linux/macOS (Bash/Zsh) and Windows PowerShell, both of which strictly adhere to the 256-character limit:

---

Linux / macOS
curl -s -X POST "http://192.168.178.192/rpc" -H "Content-Type: application/json" --data-raw '{"sn":"HOA1xxxxxxxxx","method":"HA.Mqtt.SetConfig","params":{"config":{"enable":true,"server":"192.168.178.99","port":1883,"protocol":"mqtt","username":"myuser","password":"mypassword"}}}'

---

Windows PowerShell
With Windows always use double quotes " outside and escape the inner quotes "

Important: do not use --location, otherwise curl may insert redirects and the body will be too long.

curl -s -X POST "http://192.168.178.192/rpc" -H "Content-Type: application/json" --data-raw '{"sn":"HOA1xxxxxxxxx","method":"HA.Mqtt.SetConfig","params":{"config":{"enable":true,"server":"192.168.178.99","port":1883,"protocol":"mqtt","username":"myuser","password":"mypassword"}}}'

---

A JavaScript script for ioBroker (SolarFlow 800 Plus / SF2400AC via zenSDK HTTP) can be found in the german iobroker forum.

It was originally developed to enable SmartMode:1 (Save to RAM). Subsequently, support for enabling/disabling MQTT over HTTP and additional features was added.

Currently, several HTTP POST commands exist:
POST 1: SmartMode
POST 2: MQTT over HTTP
POST 3: Generic additional data points

The script is simply structured so that existing features continue to work reliably, and the latest changes were safely integrated.

I hope this helps!