To cite package ‘royale’ in publications use:

  Kenny C (2022). _royale: Clash Royale API_. R package version 0.0.1,
  , <https://github.com/christopherkenny/royale>.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {royale: Clash Royale API},
    author = {Christopher T. Kenny},
    year = {2022},
    note = {R package version 0.0.1, 
},
    url = {https://github.com/christopherkenny/royale},
  }