Nextcloud - Collabora GuzzleHttp\Exception error

Error when connecting Nextcloud Office app to Collabora Code server.

Nextcloud 25.0.2 on https://mydomain.com
Nextcloud Office app 7.0.2
PHP 8.1
Collabora code server (latest) on separate server, https://sudomain.mydomain.com behind NGINX reverse proxy, SSL Certificate CA
A record pointing subdomain to Collabora server

Can reach Collabora server externally via https://subdomain.mydomain.com:443, result ‘OK’

Nextcloud error code

GuzzleHttp\Exception\ClientException: Client error: GET https://subdomain.mydomain.com/hosting/capabilities resulted in a 404 Not Found response: <meta name=“viewport” content="width=device-width, initial-scale=1, sh (truncated…)

etc

Any thoughts…