With mac os and r-devel, I got the following error:
Error: (converted from warning) unable to access index for repository https://cloud.r-project.org/bin/macosx/el-capitan/contrib/4.0:
cannot open URL 'https://cloud.r-project.org/bin/macosx/el-capitan/contrib/4.0/PACKAGES'
Execution halted
The command "Rscript -e 'deps <- remotes::dev_package_deps(dependencies = NA);remotes::install_deps(dependencies = TRUE);if (!all(deps$package %in% installed.packages())) { message("missing: ", paste(setdiff(deps$package, installed.packages()), collapse=", ")); q(status = 1, save = "no")}'" failed and exited with 1 during .