HoneyComb Plugin Configuration

I'm trying to implement the honeycomb plugin, I am following this guide: https://developers.cloudflare.com/pages/platform/functions/plugins/honeycomb/ But, I can't get anything to be reflected in HoneyComb. I´m using the Honeycomb API_KEY directly. The NextJS project I created with C3 from Cloudflare, then I understand that you have to add a folder called "functions" in the root of the project and inside place a _middleware file that contains the code of the example. And to compile the project I am using "pages:build": "npx @cloudflare/next-on-pages@1". Maybe I need to do some additional steps? Or what else should I consider?

Honeycomb · Cloudflare Pages docs

The Honeycomb Pages Plugin automatically sends traces to Honeycomb for analysis and observability.