Getting {"error": "invalid_grant", "error_description": "invalid code verifier"}

I'm using PKCE flow https://www.dropbox.com/developers/documentation/http/documentation#oauth2-token

in my react native expo app for generating the token.

I'm able to generate code & state value successfully after hitting this url https://www.dropbox.com/oauth2/authorize 

But when i trying to get the access token using below

```

const params = new URLSearchParams({
      code,
      grant_type: "authorization_code",
      client_id: DROPBOX_CLIENT_ID,
      code_verifier: codeVerifier,
      redirect_uri: redirectUri,
    });

    console.log("PKCE params", params.toString());

    const response = await fetch("https://api.dropboxapi.com/oauth2/token", {
      method: "POST",
      headers: {
        "Content-Type": "application/x-www-form-urlencoded",
      },
      body: params.toString(),
    });

```

I'm getting this error {"error": "invalid_grant", "error_description": "invalid code verifier"}

I've verified that the code challenge and code verifier are correct and are passed correctly into the request. 

Stuck on this for hours now, need help. Thanks