install python3-pip package first with the following command:
sudo apt install python3-pip
and then the nala package with the following command:
sudo apt install nala
and verify if nala is working correctly with:
sudo nala update
with that command nala must update from all the repository also checking if the repository are up to date.
It is also possible to create a metapackage that first installs python3-pip and then nala.