Collabora connecting but only getting basic menu and no document

I have nextcloud and collabora on the same box. Collabora vhost is 4435. loolwsd.xml has ssl to loolwsd server on localhost with internal proxy server. Loolwsd.xml has “true” “true” for ssl. Upstream I have a reverse proxy (proxy) on another gateway machine on port 443. This just has a simple proxypass directive of:
\ https:\\\
and ProxyPassReverse \ https:\\\
Proxy is open to the Internet and issues a letsencrypt cert. Office issues self signed cert that is loaded in Proxy’s trusted store.
All servers run Ubuntu 20.04 and latest apache2. There is no docker.
When I try to open a docx I get a basic menu (file, edit, insert, tools etc) but no document to edit.
The hostname in loolwsd.xml is and for wopi storage I have set “true” for proxy and and also for my static ‘external’ IP address.
Any ideas about why this is happening?
Could the problem be that WOPI storage is not accessible?
My basic question, however, is whether it is possible to have a gateway server proxying collabora and other servers (including nextcloud which works fine).
If not, would it work better to load loolwsd on the gateway proxy and remove it from the office/nextcloud instance. I am new at this and don’t even know if I can host a collabora server independently of nextcloud. I assume I can because its seems you can use a demo server and also a collabora server on a completely different domain with a different IP address.
Any help appreciated as I am ready to give up. Is it possible to pay a collabora developer to advise how to set this up with my particular configuration or pay to use a collabora server.