BYOC Edge webhook payload rejected by ServiceNow

Could use a hand troubleshooting this 403 Forbidden response from ServiceNow when the BYOC Edge node pushes a messaging:conversation:wrapup payload via a Data Action. The Authorization header is being constructed correctly in Architect v4.2, but the ServiceNow incident table API rejects the request citing invalid_token despite successful auth on standard cloud webhooks. Is there a specific header requirement for BYOC outbound requests?