I Can't connect Onlyoffice-DocumentServer to my Nextcloud

Hello, I have intalled Nextcloud and Onlyoffice-Documentserver on the same server, a Debian 9 (Stretch). I have configured NGINX and both are reachable on
https://cloud.mydomain.fr for Nextcloud
https://documents.mydmain.fr for Onlyoffice (But I have a 403 Forbidden page)

I’m surprise by the 403 error, and by the Onlyoffice’s documentserver’s folder :

[root@Debian:/var/www/onlyoffice]# ls -l documentserver
total 76
-rw-r--r--  1 ds ds  5312 sept. 30 14:22 3rd-Party.txt
drwxr-xr-x 40 ds ds  4096 oct.  28 17:19 core-fonts
drwxr-xr-x  2 ds ds  4096 oct.  28 18:10 fonts
drwxr-xr-x  2 ds ds  4096 oct.  28 18:05 license
-rw-r--r--  1 ds ds 34520 sept. 30 14:22 LICENSE.txt
drwxr-xr-x  3 ds ds  4096 oct.  28 18:05 npm
drwxr-xr-x  6 ds ds  4096 oct.  28 17:19 sdkjs
drwxr-xr-x 11 ds ds  4096 oct.  28 18:05 sdkjs-plugins
drwxr-xr-x 11 ds ds  4096 oct.  28 17:19 server
drwxr-xr-x  4 ds ds  4096 oct.  28 17:19 web-apps

No index ? No script to launch ? No php pages ? It is normal ?

When I try to connect OnlyOffive to my cloud in the Admin panel I have this error mesage

Erreur durant la tentative de connexion 
(Client error: "GET https://documents.mondomain.fr/healthcheck" 
resulted in a "404 Not Found" response: 
<html> <head><title>404 Not Found</title></head> <body bgcolor="white"> 
<center><h1>404 Not Found</h1></center> <hr> (truncated...) )

Any ideas ?

This request wants healthcheck file, but my folder not contain it, I don’t know why

Thanks