Architect Set Variable webhook to ServiceNow returning 401 Unauthorized

Context:
GC Release 2024-10. Architect flow triggers webhook.execute to update ServiceNow ticket status via Data Action. Endpoint is correct. Payload contains valid OAuth2 Bearer token.

Question:
I cannot figure out why the integration returns HTTP 401 despite valid credentials. ServiceNow logs show the request arrives but rejects the token. Is Genesys Cloud stripping headers?