x must be numeric problem in d3heatmap shiny

[stephenireland23]

when I try to produce a heatmap using the code below, in shiny an x must be numeric error appears. could anyone explain why this is based on the code below. thanks

d <-read.csv("dataset2.csv",header=TRUE,sep=",")
mat1<-as.matrix(d, nrow=10,ncol=20, byrow=TRUE,header=TRUE,sep=",")

server <- function(input, output, session) {
output$heatmap <- renderD3heatmap({
d3heatmap(
scale(mat1),
colors = input$palette,
dendrogram = if (input$cluster) "both" else "none"
)
})
}