[BUG] Anthropic Claude 3 Error Message - json { "error": true, "message": "Failed to fetch" }

### Bug Description

Any chat requests using any of the models: Sonnet, Haiku or Opus result in the error message:

```json
{
"error": true,
"message": "Failed to fetch"
}
```

### Steps to Reproduce

In settings:
Model Provider: Anthropic
Endpoint Address: https://api.anthropic.com
Anthropic API Key: Entered (verified working elsewhere)
API Version: 2023-06-01
Custom Models: left blank
Model: claude-opus-3-20240229(Anthropic)
All other settings as per default.

### Expected Behavior

Normal chat response from server.

### Screenshots


### Deployment Method

- [ ] Docker
- [ ] Vercel
- [ ] Server

### Desktop OS

Windows 10

### Desktop Browser

Firefox

### Desktop Browser Version

Windows Version 2.12.3

### Smartphone Device

_No response_

### Smartphone OS

_No response_

### Smartphone Browser

_No response_

### Smartphone Browser Version

_No response_

### Additional Logs

_No response_

No source file or test is named. Reproduce an Anthropic chat request with the listed endpoint, API version, model, and browser settings, then trace the request path that produces the “Failed to fetch” response. Done means Sonnet, Haiku, and Opus requests return normal chat responses instead of this error.

Written by the indexing model from the issue text.