If any message to assistant contains this, for example if the message has a snippet of html source, it gets "Request failed: 403" as a response:
<meta charset="utf-8">
The same 403 happens if you put that to the web search input field.
If you try to start a conversation with that, the UI does not show an error
I was trying to diagnose another error in my homelab logs, so I sent pieces of the log to assistant. The html tag mentioned above was included in the logs and the whole message was then rejected.
Sure this error is very easy to work around. I removed these <> characters and the message is accepted.
Generally I'd expect such message to be accepted, but for me this is very minor inconvenience.
But the tag is pretty common html, so anyone trying to send their html pages to assistant for any purpose, fixing, feedback etc will probably stumble on this.