---
meta:
  title: "The type you provided for 'FeedMessageData' is not a valid JSON value"
  parentTitle: "Error"
  description:
    "Your 'FeedMessageData' type is incorrect and needs to be updated"
---

## Why this error occurred

You have provided a custom `FeedMessageData` type for your application, but the
type you provided isn’t a (completely) valid JSON value. Values like `Date`,
`Map`, `Set`, functions, classes, or `unknown` aren’t valid JSON.

```ts highlight="4-8"
declare global {
  interface Liveblocks {
    FeedMessageData: {
      // Your own fields go here…
      userId: string;
      content: string;
      status: "streaming" | "complete";
      sentAt: Date; // ❌ The issue is here
    };
  }
}
```

In the example above, the problem is in the `sentAt` field, because a `Date`
isn’t a valid JSON value.

## How to fix it

You’ll need to figure out what part of your provided `FeedMessageData` type
definition isn’t valid JSON. Sometimes this is immediately obvious, like in the
example above.

Sometimes the issue may be a bit less obvious:

```ts highlight="6-7"
import type { Json } from "@liveblocks/client";

declare global {
  interface Liveblocks {
    FeedMessageData: {
      content: unknown; // ❌ Unknowns could contain non-JSON
      content: Json; // ✅ Prefer using Json
    };
  }
}
```

By using `Json`, you can still work with unknown or unspecified values, but
still ensure they will be valid JSON.

## If you cannot find the root cause

Sometimes types can be complex and the root cause is still unclear. In those
cases, there is a small trick you can use. Try to assign your type to the
required base type, with this line:

```ts highlight="9-10"
import type { Json } from "@liveblocks/client";

declare global {
  interface Liveblocks {
    FeedMessageData: MyFeedMessageData;
  }
}

// Quick debugging snippet to find root cause
const xxx: Json = {} as MyFeedMessageData;
//    ^?
//    The error will appear here
```

Now TypeScript will explain why it thinks your type isn’t valid JSON:

```error showLineNumbers={false}
Type 'MyFeedMessageData' is not assignable to type 'Json'.
  Type 'MyFeedMessageData' is not assignable to type 'JsonObject'.
    Property 'sentAt' is incompatible with index signature.
      Type 'Date' is not assignable to type 'Json | undefined'.
        Type 'Date' is not assignable to type 'JsonObject'.
          Index signature for type 'string' is missing in type 'Date'.
```

---

For an overview of all available documentation, see [/llms.txt](/llms.txt).