Unable to git add <file> using system2 from R script

Question

I am trying to add a file using git add. Note: I am very new to git.

Using Ubuntu Linux

From a terminal prompt, this works.

/usr/bin/git add static/fb/img/gic1-5_yield_curve_5bd11b935bd72745.png

I can confirm that it works by doing git status and seeing the filename under, Changes to be committed:

I want to be able to do the same thing from an R script. This does not work:

system2(command = "/usr/bin/git", args = c("add", "static/fb/img/gic1-5_yield_curve_5bd11b935bd72745.png"))

Why is this?