Worker fetch to subdomain does not work

I have a worker that’s under Within the worker, there’s a fetch pointing to DNS for the domain is handled by Cloudflare. The worker is obviously hosted there, but the external endpoint is an A record pointing to an external API (i.e.

No matter what I do, that request never fires. Using the original endpoint ( works just fine. And using that API as works just fine outside the Worker.

The problem is specifically within the Worker, trying to fetch a same domain endpoint. Is there something I need to do on Cloudflare to make this work or is it simply not possible?