Error: Unhandled Exception: Child Task 765743448 failed: Error building image: Error fetching highr (0.8.1) source. <CRANPackageSource repo='http://cran.rstudio.org'> unable to satisfy package: highr (0.8.1)
The current version of highr on CRAN is 0.8, which is older than the 0.8.1 you requested. Do you need the most recent features in 0.8.1? If not, I assume there's some way in Shiny to say you only need highr version 0.8.
If you want more detailed information, please tells us more about what you've tried and what is broken, rather than only supplying the error message.