post https://dathost.net/api/0.1/game-servers//files/
The path is counted from the root node as seen in the file manager in the control panel,i.e. to write csgo/cfg/server.cfg the path would be cfg/server.cfg, if the path ends with / a directory will be created and the file parameter will be ignored.
There is a upload limit of 100MB on dathost.net, use FTP to upload bigger files.