ここの指示に従ってTに行きました
https://cran.r-project.org/bin/windows/Rtools/
jsonlite パッケージでテストを実行すると、まだ取得します
WARNING: Rtools is required to build R packages but is not currently installed. Please download and install the appropriate version of Rtools before proceeding:
その後
Error: ERROR: no permission to install to directory 'C:/Users/fl014036/Documents/R/R-3.6.2/library'
Warning in install.packages :
installation of package ‘jsonlite’ had non-zero exit status