To cite package ‘sp23design’ in publications use:

  Narasimhan B, Shih M, He P (2022). _sp23design: Design and Simulation
  of Seamless Phase II-III Clinical Trials_. R package version 0.9-1,
  <https://CRAN.R-project.org/package=sp23design>.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {sp23design: Design and Simulation of Seamless Phase II-III Clinical Trials},
    author = {Balasubramanian Narasimhan and Mei-Chiung Shih and Pei He},
    year = {2022},
    note = {R package version 0.9-1},
    url = {https://CRAN.R-project.org/package=sp23design},
  }