PLUGIN_CLIENT_CONFIG_NOT_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

✗ 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)