To cite package ‘freecurrencyapi’ in publications use:

  Kukacka D (2023). _freecurrencyapi: Client for the
  'freecurrencyapi.com' Currency Conversion API_. R package version
  0.1.0, , <https://CRAN.R-project.org/package=freecurrencyapi>.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {freecurrencyapi: Client for the 'freecurrencyapi.com' Currency Conversion API},
    author = {Dominik Kukacka},
    year = {2023},
    note = {R package version 0.1.0, },
    url = {https://CRAN.R-project.org/package=freecurrencyapi},
  }