What happened is this:
I built a program using Shiny. But in this program, I am also using openxlsx in order to print my results in an excel file using write.xlsx(). So at the very top of my server.R file, I wrote this piece of code:
Sys.setenv("R_ZIPCMD" = "C:/Rtools/bin/zip.exe")
library(openxlsx)
When I run it in my computer, it worked just fine. But when I deployed it into the cloud (using shinyapps.io) and run it in another computer (using a Chrome), I got this error:
*Error: zipping up workbook failed. Please make sure Rtools is installed or a zip application is available to R. Try installr:: install.rtools() on Windows.*