### Check for existing issues

- [x] I have searched the existing issues and checked that my issue is not a duplicate.

### What happened?

Attempting to modify the budget of a virtual key, and saving that setting results in an error: see screenshot below

<img width="402" height="288" alt="Image" src="https://github.com/user-attachments/assets/9c815e4a-f8c5-454e-b5e8-d8cf6fb623e8" />

Not sure if this is expected behavior since until a very recent versions such modifications were allowed.

*Note:* Adding a budget (if undefined) to an already existing virtual key is allowed; but editing that amount a moment later is not, and results in the error above.

### Steps to Reproduce

1. Go to the virtual keys tab 2. Select a virtual key (any) 3. Go to settings tab and then click the "Edit settings" blue button 4. Edit the budget (it needs to be non-zero). 5. Click "Save settings" & observe the error!

### Relevant log output

```shell

```

### What part of LiteLLM is this about?

UI Dashboard

### What LiteLLM version are you on ?

v1.82.3

### Twitter / LinkedIn details

_No response_