[field troubleshooting]: use EITHER ELASTIC_API_KEY OR APM_SECRET_TOKEN, not both; for Elastic Cloud prefer the API key. Check the API key format (base64 string) and that it has APM permissions. 'No application was found' in the APM app simply means no data has arrived yet: verify the app is running, generate some traffic, confirm the service name matches what you configured, and wait 30-60 seconds for indexing before refreshing. Verify OTLP variables are all set when no observability data appears.

Context: APM agent authentication fails or behaves unexpectedly. Elastic Cloud expects exactly one auth method.