Connction to Nextcloud, no SSL, no DNS

Hi there, i’m trying to set up nextcloud server connected to the on premise community onlyoffice document server on local LAN.
I did try docker, as well as separate ubuntu servers. Nextcloud works fine, docserver healthcheck also is true. Even connectivity from nextcloud to doc server checked with Curl looks OK.
I was trying to use self signed certificates as well as just http, since those server will not be available from outside of the LAN. There is no DNS, so I’m using either localhost or private IP.
Problem is of course when I try to connect to the doc server from nextcloud settings there is usually error: error when trying to connect (error occurred in the document service: error while downloading the document file to be converted.) (version 8.2.0.143).
I’ve watched a dozen of tutorials, read official doc., nothing helps.
Maybe anybody here had successfully connected on premise onlyoffice doc server to nextcloud with self signed SSL or without SSL and can share some config tips or files like nextcloud config.php or onlyoffice local.json? Is setup like this even possible?

You can disable certificate validation in the Nextcloud connector settings by using the option “disable certificate validation.”
A link to all configuration parameters and explanations is provided below:

To disable certificate verification by DocumentServer, change the rejectUnauthorized parameter in the configuration file default.json from true to false.

The file is located at:

Linux: /etc/onlyoffice/documentserver/default.json
Windows: C:\Program Files\ONLYOFFICE\DocumentServer\config\default.json

If these instructions don’t help, you can send a screenshot with the errors, and we’ll try to troubleshoot further.