Using the latest GitHub version (4.9.2.9000) of plotly, shiny 1.5.0 and htmlwidgets 1.5.2 the provided example gives: > Error in (function (outputId, name, width, height, package = name, inline = FALSE, : > unused argument (reportTheme = TRUE) ``` library(shiny) library(plotly) ui <- fluidPage( plotlyOutput("testPlot") ) server <- function(input, output, session) { plot_ly(y = 1:10, type = "scatter", mode = "lines") } shinyApp(ui, server) ``` The problem seems to be [introduced](https://github.com/ropensci/plotly/pull/1802) [here](https://github.com/ropensci/plotly/commit/36e2928904ee92ed48b95c31c01545107a9e728e): ``` if (is_available("shiny", "1.4.0.9003") && is_available("htmlwidgets", "1.5.1.9001")) { args$reportTheme <- reportTheme } ``` `reportTheme` is available [since htmlwidgets 1.5.2.9000](https://github.com/ramnathv/htmlwidgets/blob/master/inst/NEWS) not 1.5.1.9001.