Cannot Install Theme – Requires FTP access

I’m trying to install a theme on WordPress but asking for FTP credentials. Our server (IP address, no domain yet — XX.XX.XXX.XXX) was accessed by SFTP (on a specific folder) and then used “sudo su” to gain root access. Configured wp-config.php and put in DB name, username and password and thought it’d be a good start.

I’ve tried using the IP as hostname and used the username & password I had but it has an error saying – “Failed to connect to FTP Server XX.XX.XXX.XXX”. I also tried using localhost but has the same error.

I’ve searched for different solutions in the web to install themes without FTP credentials like the “direct” thing but it’s not working. Can anyone help me? Thanks!