Failed on Running the Spacefold Demo Locally

I followed the instructions of ``[Running the Spacefold Demo Locally](https://github.com/connext/spacefold#running-the-spacefold-demo-locally)'' but it failed with JSON parsing error.

```
>> yarn build
yarn run v1.22.10
$ next build && next export
info - Creating an optimized production build
info - Compiled successfully

> Build error occurred
SyntaxError: Unexpected token u in JSON at position 0
```

The commands I ran are
1. clean clone this repo and then cd in
2. `yarn install`
3. `yarn build` -> trigger error
3.1. if I skip 3. to run `yarn start`, it tells me there's no build file.
```
>> yarn start
yarn run v1.22.10
$ next start
Error: Could not find a production build in the '$HOME/spacefold/.next' directory. Try building your app with 'next build' before starting the production server. https://err.sh/vercel/next.js/production-start-no-build-id
```

Can someone point me out how to build it? appreciate it!