The write key was rejected

What you see

In the browser console or your server log, one of:

writeKey is not a write key (togo_pkt_… or togo_pkl_…). Check for an unsubstituted environment variable. No events will be captured.
writeKey is a SECRET key, not a write key. …
… the write key was rejected (401). No events will be captured on this page. …

or, from the ingest endpoint, a 401 with missing_write_key or invalid_write_key.

The usual causes

1. The environment variable did not reach the build. The most common one. The value is empty or still the literal process.env.… text. Frameworks only ship variables with their public prefix to the browser — NEXT_PUBLIC_ in Next.js, VITE_ in Vite — and only those set when the build ran. Set it in your hosting provider’s settings for the right environment, then rebuild.
2. A secret was pasted where the write key belongs. Togo write keys start with togo_pkt_ (test) or togo_pkl_ (live). Anything else is not one — and if a secret key has shipped in a browser bundle, rotate it.
3. The key was revoked. A revoked key is refused. Find the project’s current keys in its Settings in app.togohq.ai, or ask your agent to call list_projects.
4. The key was created moments ago. A new key can take a short while to be accepted everywhere. The browser SDK keeps queued events on the device and retries them on the next page load, so reload once.

What happens to events meanwhile

The browser SDK stops sending for the rest of the page, keeps every track() call returning normally, and keeps the events it had already queued for the next page load. Nothing is sent under a key that was refused.

Check the fix

Rebuild, reload, and send one event with the test key: it should appear in Events → Live View within seconds (Check that events arrive).