I am trying to upload a shiny app that runs in my Mac to shiny io. The process works well right up until I get the following error:

Configuration failed because libarchive was not found. Try installing:

• deb: libarchive-dev (Debian, Ubuntu, etc)
• rpm: libarchive-devel (Fedora, CentOS, RHEL)
• csw: libarchive_dev (Solaris)
• brew: libarchive (Mac OSX)
  If libarchive is already installed, check that ‘pkg-config’ is in your
  PATH and PKG_CONFIG_PATH contains a libarchive.pc file. If pkg-config
  is unavailable you can set INCLUDE_DIR and LIB_DIR manually via:
  R CMD INSTALL –configure-vars=’INCLUDE_DIR=… LIB_DIR=…’

• installing to library ‘/usr/lib/R’
• installing source package ‘archive’ …
  ** package ‘archive’ successfully unpacked and MD5 sums checked
  ** using staged installation
  :1:10: fatal error: archive.h: No such file or directory
  compilation terminated.
  ERROR: configuration failed for package ‘archive’
• removing ‘/usr/lib/R/archive’

I checked using “brew ls” that libarchive is indeed installed. So I imagine the problem lies with the pkg-config not being in my PATH and/or the PKG_CONFIG_PATH not containing a libarchive.pc.file. But I have no idea what the PATH is, or how to find said PATH in my MAC, let alone what it means by the PKG_CONFIG_PATH. I have searched online but have been unable to find a solution, so any help would be much appreciated – if possible one that would be as simple as possible given my lack of knowledge.