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.

Context: GitHub issue team-telnyx/telnyx-node#194: In 2.0.0-beta.5 the WebhookHeader was a Uint8Array in the source but typed as a string in the published type declarations, so calling verifySignature produced type errors. The reporter noted that string could not even work as-is because the internals needed a Uint8Array. A contributor confirmed the mismatch and shipped a fix; the issue was resolved in 2.0.0-beta.6 and 2.0.0.