Access to cran packages

I am able to access R packages on my laptop, but not on my desktop computer. Both are Macs, both running OS10.13.6 High Sierra. When I open package installer on the laptop and click"Get list" it provides the usual list of packages. On the desktop computer (Mac Pro Tower, 2012) the following message pops up in the R console window:
"Warning: unable to access index for repository https://cran.stat.auckland.ac.nz/bin/macosx/contrib/4.2:
  cannot open URL 'https://cran.stat.auckland.ac.nz/bin/macosx/contrib/4.2/PACKAGES'

The same happens if I type >install.packages() into the R console window. A list of packages appears on the laptop, but on the desktop computer this happens:

install.packages()

Warning: unable to access index for repository https://cran.stat.auckland.ac.nz/src/contrib:
  cannot open URL 'https://cran.stat.auckland.ac.nz/src/contrib/PACKAGES'
Error in install.packages() : argument "pkgs" is missing, with no default

install.packages(sf)

Error in install.packages(sf) : object 'sf' not found

Both computers are online, and on both of them I can see the list of packages here: https://cran.stat.auckland.ac.nz/bin/macosx/contrib/4.2/PACKAGES

Is there a way to directly download the packages?

Many thanks!

Liz Slooten
Professor Emeritus, University of Otago, New Zealand