# PLUGIN_CLIENT_CONFIG_NOT_JSON

A plugin's `admin.clientConfig` holds a value that cannot be sent to the browser as JSON.

## Cause

A plugin's `admin.clientConfig` holds a value that cannot be sent to the browser as JSON.

A plugin's `contributes.admin.clientConfig` is sent to the admin as JSON. A function, class instance, `Date` or `Map` in it would arrive changed or missing, so it is refused when the configuration loads. The message names the keys at fault.

## Fix

* Remove the keys listed from `clientConfig`, or give them values of strings, numbers, booleans, null, arrays or plain objects.
* If the plugin is not yours, update it to a release whose client configuration is plain JSON.

## Example

```text
✗ Plugin "reviews" declares an admin.clientConfig that is not JSON (keys: onSave).
  Why:  It is serialized into /api/admin-meta, so it may hold only strings, numbers, booleans, null, arrays and plain objects — no functions, class instances, Dates or Maps.
  Next: Remove `onSave` from `contributes.admin.clientConfig`, or give it a value of strings, numbers, booleans, null, arrays or plain objects.
  Docs: https://nextlyhq.com/docs/cli/errors/plugin-client-config-not-json  (PLUGIN_CLIENT_CONFIG_NOT_JSON)
```