Cart Attributes Note in Checkout

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Hello Community, i am trying to setup my checkout to be able to add some variable to the cart attribute. I've made a javascript script to populate those attributes following the tutorial:

It should be very simples, but i can't reach those variables in shopify admin. This is a example of a checkout url that should work.[test]=true

I'am doing something wrong? Something has changed and this feature is not working anymore?