## TL;DR

Upgrade to 2.0.0-beta.6 or 2.0.0, where the declarations match the implementation. A contributor confirmed the mismatch and shipped a fix; the issue was resolved in 2.0.0-beta.6 and 2.0.0.

## Steps

1. If TypeScript rejects your Telnyx verifySignature call over the WebhookHeader type, check your SDK version before casting around it. Beta 5 shipped mismatched types (string in the declarations, Uint8Array in the implementation). Upgrade to 2.0.0-beta.6 or 2.0.0, where the declarations match the implementation.

## When to use

You are seeing this: If TypeScript rejects your Telnyx verifySignature call over the WebhookHeader type, check your SDK version before casting around it. Use this skill when you run into "Telnyx WebhookHeader type mismatch in 2.0.0 betas: fixed in beta.6".

## 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: 2.0.0-beta.6, 2.0.0, 2.0.0-beta.5. If you are on something much newer or older, the details may have shifted.

## Why this happens

The original report does not dig into a root cause. It documents the symptom and the fix that resolved it.