Unable to deploy shiny app - unable to access index for repository CRAN

I'm very new to Shiny, so this could be a simple mistake on my part. I'm getting a warning when I try to deploy the app that there is a probelm accessing the CRAN repository. This is the warning:

Warning: unable to access index for repository https://cran.rstudio.com/src/contrib:
  cannot open URL 'https://cran.rstudio.com/src/contrib/PACKAGES
...
* Unable to determine the location for some packages. Packages must come from a package repository like CRAN or a source control system.
   Check that options('repos') refers to a package repository containing the needed package versions.

Oddly, the warning lists out the warning for every library I've ever installed (where I inserted "..." above), although I'm only using a couple libraries in my app:

  • library(quantmod)
  • library(tidyverse)
  • library(shiny)
  • library(plotly)

When I run options('repos'), I get this:

$repos
                       CRAN 
"https://cran.rstudio.com/" 
attr(,"RStudio")
[1] TRUE

Has anyone had a similiar problem? Or have a suggestion on how to get my app to deploy? Thanks in advance!