trackOpen() fails with "JSON Parse error: Unexpected character: o" on React Native due to fetch polyfill auto-parsing

[dbezrukov]

Description

The trackOpen() method fails on React Native with JSON Parse error: Unexpected character: o even when the API returns a valid JSON response with clickId.

Root Cause

React Native's fetch polyfill automatically parses JSON responses when content-type: application/json is present. When the SDK calls response.json() in trackOpen(), the response body is already a parsed JavaScript object, not a string. Calling .json() on an already-parsed object causes it to be implicitly converted to "[object Object]", which then fails JSON parsing with "Unexpected character: o".

Reproduction

1. Install @dub/react-native in a React Native app
2. Initialize with dub.init({ publishableKey, domain })
3. Copy a valid Dub link to clipboard (e.g., https://go.customuse.com/test)
4. Call dub.trackOpen() on first launch
5. Observe the error: JSON Parse error: Unexpected character: o

Evidence

Direct API call using XMLHttpRequest with responseType = 'text' works correctly:

// This works - returns valid JSON with clickId
const xhr = new XMLHttpRequest();
xhr.open('POST', 'https://api.dub.co/track/open', true);
xhr.responseType = 'text';
xhr.onload = () => {
  const data = JSON.parse(xhr.responseText); // ✅ Works
  console.log(data.clickId); // "MT3ka2lKYidkICLm"
};

Suggested Fix

Option 1: Use XMLHttpRequest with responseType = 'text' instead of fetch
Option 2: Check if the response body is already an object before calling .json()

const response = await fetch(url, options);
const body = await response.text();
return typeof body === 'object' ? body : JSON.parse(body);

Environment

@dub/react-native: 0.0.2
React Native: 0.76.x
Platform: iOS (likely affects Android too)
Expo SDK: 52