AWS Cognito - I am refreshing token using adminInitiateAuth() method, but its giving eror "unable to verify secret hash"

AWS Cognito - I am refreshing token using adminInitiateAuth() method, but its giving error "unable to verify secret hash".

I am using PHP SDK

The same secret hash is working on signing user. Below is the return response AWS Cognito -

```"message": "Error executing \"AdminInitiateAuth\" on AWS HTTP error: Client error: `POST` 
           Unable to verify secret hash for client```

HASH GENERATION

public function cognitoSecretHash($username){
        $hash = hash_hmac(
            'sha256',
            $username. $this->client_id,
            $this->client_secret,
            true
        );
        return base64_encode($hash);
    }


       $response = $this->client->adminInitiateAuth([ 
                'AuthFlow' => 'REFRESH_TOKEN_AUTH', 
                'AuthParameters' => [
                    'USERNAME' => $username,
                    'REFRESH_TOKEN' => $refreshToken,
                    'SECRET_HASH' => $this->cognitoSecretHash($username)
                ],
                'ClientId' => $this->client_id,
                'UserPoolId' => $this->userpool_id
            ])->toArray();