## TL;DR

Check your version of Cloudflare Workers AI first , maintainers often fix the underlying bug in a later release, and the thread may predate it.

## Steps

1. [petebacondarwin (contributor)]: Underscores in worker names break TLS hostname verification (test_worker.subdomain.workers.dev fails the check), which breaks wrangler dev --remote and Miniflare fetches. Rename the worker to remove the underscore: do it in the Cloudflare dashboard (Workers -> Manage -> Rename Worker), not by renaming in wrangler.toml, which would orphan the old worker. zehawki confirmed the dashboard rename fixed it with no data loss.

2. This comes from one real issue thread (https://github.com/cloudflare/workers-sdk/issues/4921); it is the verified fix or approach from that thread, not a general manual. Check your version of Cloudflare Workers AI first , maintainers often fix the underlying bug in a later release, and the thread may predate it.

## When to use

You are seeing this: Issue cloudflare/workers-sdk#4921 (closed, 35 comments): ### Which Cloudflare product(s) does this pertain to? Use this skill when you run into "🐛 BUG: Unable to run wrangler dev since version 3.19.0".

## When not to use

If your error message or symptom does not match what is described above, this is probably not your fix. Search for your exact error text instead of forcing this one to fit.

## Versions

Versions mentioned in the source: using 3.26.0, using 20.11.0, 3.19.0. If you are on something much newer or older, the details may have shifted.

## Why this happens

Issue cloudflare/workers-sdk#4921 (closed, 35 comments): ### Which Cloudflare product(s) does this pertain to?

## Sources

- https://github.com/cloudflare/workers-sdk/issues/4921