Yeah I did. Just to follow Rtools's guide, I ran Sys.which("make") and the console showed
make
"C:\rtools40\usr\bin\make.exe"
but when I tried install.packages("jsonlite", type = "source"), I get
Installing package into ‘C:/Users/user/Documents/R/win-library/4.1’
(as ‘lib’ is unspecified)
trying URL 'https://cran.rstudio.com/src/contrib/jsonlite_1.7.2.tar.gz'
Content type 'application/x-gzip' length 421716 bytes (411 KB)
downloaded 411 KB
Warning in install.packages :
installation of package ‘jsonlite’ had non-zero exit status
The downloaded source packages are in
‘C:\Users\user\AppData\Local\Temp\Rtmpch3Yvc\downloaded_packages’
I'm not sure if this should be a concern. I ran...
and the binary installed sucessfully!
I'm not sure if I can continue asking this but I would like to run devtools::install_github("doomlab/MeMoBootR"), but as you can see below, it still fails. 
Downloading GitHub repo doomlab/MeMoBootR@HEAD
Installing 12 packages: colorspace, viridisLite, RColorBrewer, munsell, labeling, farver, scales, isoband, gtable, shape, ggplot2, diagram
Installing packages into ‘C:/Users/user/Documents/R/win-library/4.1’
(as ‘lib’ is unspecified)
trying URL 'https|COLON|//cran.rstudio.com/bin/windows/contrib/4.1/colorspace_2.0-1.zip'
Content type 'application/zip' length 2640934 bytes (2.5 MB)
downloaded 2.5 MB
trying URL 'https|COLON|//cran.rstudio.com/bin/windows/contrib/4.1/viridisLite_0.4.0.zip'
Content type 'application/zip' length 1299475 bytes (1.2 MB)
downloaded 1.2 MB
trying URL 'https|COLON|//cran.rstudio.com/bin/windows/contrib/4.1/RColorBrewer_1.1-2.zip'
Content type 'application/zip' length 55593 bytes (54 KB)
downloaded 54 KB
trying URL 'https|COLON|//cran.rstudio.com/bin/windows/contrib/4.1/munsell_0.5.0.zip'
Content type 'application/zip' length 244972 bytes (239 KB)
downloaded 239 KB
trying URL 'https|COLON|//cran.rstudio.com/bin/windows/contrib/4.1/labeling_0.4.2.zip'
Content type 'application/zip' length 62808 bytes (61 KB)
downloaded 61 KB
trying URL 'https|COLON|//cran.rstudio.com/bin/windows/contrib/4.1/farver_2.1.0.zip'
Content type 'application/zip' length 1752105 bytes (1.7 MB)
downloaded 1.7 MB
trying URL 'https|COLON|//cran.rstudio.com/bin/windows/contrib/4.1/scales_1.1.1.zip'
Content type 'application/zip' length 563213 bytes (550 KB)
downloaded 550 KB
trying URL 'https|COLON|//cran.rstudio.com/bin/windows/contrib/4.1/isoband_0.2.4.zip'
Content type 'application/zip' length 3062282 bytes (2.9 MB)
downloaded 2.9 MB
trying URL 'https|COLON|//cran.rstudio.com/bin/windows/contrib/4.1/gtable_0.3.0.zip'
Content type 'application/zip' length 434074 bytes (423 KB)
downloaded 423 KB
trying URL 'https|COLON|//cran.rstudio.com/bin/windows/contrib/4.1/shape_1.4.6.zip'
Content type 'application/zip' length 789210 bytes (770 KB)
downloaded 770 KB
trying URL 'https|COLON|//cran.rstudio.com/bin/windows/contrib/4.1/ggplot2_3.3.3.zip'
Content type 'application/zip' length 4070136 bytes (3.9 MB)
downloaded 3.9 MB
trying URL 'https|COLON|//cran.rstudio.com/bin/windows/contrib/4.1/diagram_1.6.5.zip'
Content type 'application/zip' length 682763 bytes (666 KB)
downloaded 666 KB
package ‘colorspace’ successfully unpacked and MD5 sums checked
package ‘viridisLite’ successfully unpacked and MD5 sums checked
package ‘RColorBrewer’ successfully unpacked and MD5 sums checked
package ‘munsell’ successfully unpacked and MD5 sums checked
package ‘labeling’ successfully unpacked and MD5 sums checked
package ‘farver’ successfully unpacked and MD5 sums checked
package ‘scales’ successfully unpacked and MD5 sums checked
package ‘isoband’ successfully unpacked and MD5 sums checked
package ‘gtable’ successfully unpacked and MD5 sums checked
package ‘shape’ successfully unpacked and MD5 sums checked
package ‘ggplot2’ successfully unpacked and MD5 sums checked
package ‘diagram’ successfully unpacked and MD5 sums checked
The downloaded binary packages are in
C:\Users\user\AppData\Local\Temp\Rtmpch3Yvc\downloaded_packages
Error: Failed to install 'MeMoBootR' from GitHub:
System command 'Rcmd.exe' failed, exit status: -1, stdout + stderr empty
Note: I replaced ":" with |COLON| in the above console output.