> ## Documentation Index
> Fetch the complete documentation index at: https://docs.duelduck.com/llms.txt
> Use this file to discover all available pages before exploring further.

# POST /duel/solana/join/sign-tx

**URL:** [https://xapi.duelduck.com/duel/solana/join/sign-tx](https://xapi.duelduck.com/duel/solana/join/sign-tx)

Creates a signed transaction that allows a user to join an app-based crypto prediction.

### **Parameters**

| Name          | Type   | Header        | Required | Description                |
| :------------ | :----- | :------------ | :------- | :------------------------- |
| Authorization | string | Authorization | yes      | Authorization Bearer token |

### **Request**

Prediction join request.

**Type:** object. **Request content type:** application / json . Body:

```text theme={"dark"}
{
  "answer": 0,
  "duel_id": "string",
  "external_source": "string",
  "invited_by": "string",
  "paid_price": 0
}
```

### **Responses**

**Response content type:** application / json .

#### Code 200

Signed transaction returned successfully.

```text theme={"dark"}
{
  "tx": "string"
}
```

#### Code 400

Invalid request data.

```text theme={"dark"}
{
  "message": "string",
  "status": 0
}
```

#### Code 401

Unauthorized - Invalid or missing claims.

```text theme={"dark"}
{
  "message": "string",
  "status": 0
}
```

#### Code 500

Internal server error.

```text theme={"dark"}
{
  "message": "string",
  "status": 0
}
```