Hi @cthielen
You’ll need the dev version 4.7.1.900 - install with devtools::install_github("ropensci/plotly")
Plotly’s latest CRAN release 4.7.1 uses an older version of plotly.js (v1.29.2). Whereas, scatterpolar trace type were added in plotly.js v1.33.0. The dev version (4.7.1.900) of the R package uses the latest plotly.js release (v1.35.2)