Nextcloud + Collabora Online = SSL problem + 404

Nextcloud 12.0.3
Synology NAS
Apache 2.4
PHP 5.6

Access internal: directly
Access external: via Apache Reverse Proxy

I am facing problems with Collabora Onlineā€¦getting the following error in log:

Error richdocuments GuzzleHttp\Exception\ClientException: Client error response [url] [status code] 404 [reason phrase] Not Found

Error internet_connection_check GuzzleHttp\Exception\RequestException: cURL error 60: SSL certificate problem: unable to get local issuer certificate

I give it a try to google, and found suggestions to place SSL cert to path: \nextcloud\resources\config\ca-bundle.crt

anyone facing same problems?