gnome - Cannot install nvidia graphics driver 390 on Ubuntu 18.04

After facing issues with nvidia 396, I wanted to move back to nvidia 390 on Ubuntu 18.04.
I purged nvidia from the system, moving back to the default xorg driver.

I then added the repository ($ sudo add-apt-repository ppa:graphics-drivers/ppa ), and tried to install 390 by

$ sudo apt install nvidia-driver-390

However, this is also installing nvidia 396 on my machine.
How can I install 390?

Thanks.

Solved.
What was happening was that another ppa was interfering and the download was taking place from that repo.

It was the System76 Pop repository. I removed it from Software and Updates.

After that, running

$ sudo apt install nvidia-driver-390

installs the 390 driver as expected.