Pritunl client stops working in Ubuntu 20.04. Now it supports Ubuntu 24.04 and 24.10 only.
So I have to install pritunl client cli to connect to Pritunl VPN server.

In the Pritunl server, open the Temporary url to view profile link,set up Two-step authentication key, it will be used as the password

Install: apt install pritunl-client

After downloading the Profile and save in the machine, we need to add the profile with the command:
$ pritunl-client add path_to_your_profile

Another instruction:
$ printunl-client add profile_url (not work for me)

Check the profile id
Then run $ pritunl-client list to see the Profile Id

Start the VPN connection
$ pritunl-client start your_profile_id

It will fail to connect unless a password is provided. Use the code in the authentication app.
Update the above command password option
$ pritunl-client start your_profile_id --password=your_authentication_code