Collabora on Nextcloud snap: WOPI discovery URL?

Nextcloud version: 13.0.8 (snap package)
Operating system and version: Ubuntu 16.04.4 x64

I’m running Nextcloud on a Digitalocean droplet + domain. Here’s what I did to get Collabora working on my subdomain:

  1. Configured a subdomain in my DNS settings, made Nextcloud trust the subdomain and addes the subdomain to my letsencrypt config
  2. Installed the Collabora Online server
  3. Installed the Apache reverse proxy
  4. To configure a VirtualHost I used the example on the page mentioned earlier. I filled in my subdomain and deleted the SSL config.
  5. I entered the subdomain in the Collabora app setup in Nextcloud
  6. Opening a document gives me the following error in my Nextcloud log:

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

I guess I need to set the right path in my VirtualHost config, currently it is hosting/discovery… but what’s the right WOPI discovery URL? Can’t find it…

Thanks in advance for your help!