I can not connect to nextcloud with the onlyoffice Android app via WebDAV, I use the server’s crazy ip for example http: //my_ipaddress/remote.php/webdav/
Likely to be HTTPS with the s from secure. Else more information is required regarding accessibility of IP address (behind firewalls, NAT) etc. Has provider opened up it properly. Is it just you? Just a few things to start tracing down the toot cause of the issue.