it looks like reverse proxy doesn’t know where to route this request… maybe the reverse proxy config is still incomplete. Looking at Collabora reverse proxy guide I see many special config - not sure this is required for built-in CODE as well… I would start with proxy_set_header Host $http_host; I don’t see it in your config…
There was working Apache reverse proxy example linked to the above guide… the solution is not very clear but two different working Apache configs
another weird issue there is a /lool/ piece in the URI while CODE switched to /cool/ long time ago…