Forge Modpack via vps server - starting issues

I got a vps server via oracle cloud and I want to play the atm9 tts modpack on it. I am using Putty and FileZilla to access the server remotely (ssh connection).

-he server is running ubuntu
-ports have been forwarded
-openjdk-17-jdk-headless is installed (Java version for minecraft 1.20.1)

Then I tried the following:

1.method:
-I created a directory for the modpack
-I got the modpack server file from the curseforge website via "wget" and unzipped it in the directory
-I got the server installer .jar from forge for mc 1.20.1 wia "wget"
-I tried running the java file with the following command:
java -Xmx16g -Xms16g -jar forge-1.20.1-47.3.0-installer.jar
-I also tried the following commands:
java -Xmx16g -Xms16g -jar forge-1.20.1-47.3.0-installer.jar nogui
java -Xmx16g -Xms16g -jar forge-1.20.1-47.3.0-installer.jar -nogui

First command gives me the following error:

"java.awt.HeadlessException:

No X11 DISPLAY variable was set,

but this program performed an operation which requires it."

The other command give me the following error:

"Exception in thread "main"

joptsimple.UnrecognizedOptionException: n is not a recognized option"

2.method:

-I downloaded the modpack server file from curseforge to my local computer.
-I ran the startserver.bat file which was succesful and created the .jar file
-I zipped the file, uploaded it to the server via Filezilla and tried running the server with the above commands
-I get the same error codes.

Can someone help me with setting up ATM9 TTS on my vps ubuntu server? I am open to a completely different approach.