"configuration failed for package <name>"

I have recently built and R package for my online course. However, when I run travis-ci build, it grounds to a halt due to the following error:

ERROR: configuration failed for package ‘gert’

* removing ‘/home/travis/R/Library/gert’

Error in i.p(...) : 

  (converted from warning) installation of package ‘gert’ had non-zero exit status

Calls: <Anonymous> ... with_rprofile_user -> with_envvar -> force -> force -> i.p

Execution halted

The command "Rscript -e 'deps <- remotes::dev_package_deps(dependencies = NA);remotes::install_deps(dependencies = TRUE);if (!all(deps$package %in% installed.packages())) { message("missing: ", paste(setdiff(deps$package, installed.packages()), collapse=", ")); q(status = 1, save = "no")}'" failed and exited with 1 during .

Your build has been stopped.

I would appreciate it if you could give me some hints on how to pass this test.
I also run R cmd check on my package and the only warning I receive is the following:

WARNING
  'qpdf' is needed for checks on size reduction of PDFs

However, this check in also halted.

I will also leave my github package address:

configuration failed” usually means that the R package needs headers for some C libraries to be built.

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