Hi @Giovann_G 

I tried clearing the cache and also try in incognito window in Chrome and Firefox browser but no success. 

I also try with creating new Quickbook account from scratch and created sandbox company with "QuickBooks Online Advanced" but still I don't see custom field section in setting under lists section. 

I created Quickbook account from scratch using this signup page https://accounts.intuit.com/signup.html?offering_id=Intuit.devx.devx&redirect_url=https%3A%2F%2Fdeve...

Can you guys try creating new Quickbook development account from scratch and create sandbox company. And see if you can see the custom field option under Lists section?

I am attaching screenshot of incognito window.