Zotero Streaming API - Subscription does not work

I have tried to use the streaming API via different websocket clients to access a backup system of the Zotero data.
I have created an API key that has all the rights that are possible.

As suggested here, I sent the following message, as in the example:
```json {
    "action": "createSubscriptions",
    "subscriptions": [
        {
            "apiKey": "abscdeokasdopasdkas",
            "topics": [
                "/groups/1234567"
            ]
        }
    ]
}
```

or

```json {
    "action": "createSubscriptions",
    "subscriptions": [
        {
            "apiKey": "abscdeokasdopasdkas"
        },
        {
            "topics": [
                "/users/1234567"
            ]
        }
    ]
}
```
Handshake works and I get the following message back:
`{"event":"connected","retry":10000}`

But if I then send a “createSubscriptions” request, I get no response from the server.

I tried several times, with different API keys and different API Key rights settings. I created an additional library to see if it works with this one. Unfortunately not. I have tried various clients.

I would be very grateful to get a solution or find out what I am doing wrong?

Thank you very much