could not find function "flextable_to_rmd"

library(flextable)
ft <- flextable(head(mtcars))
ft <- autofit(ft)

for(i in 1:2){
  flextable_to_rmd(ft)
}

Error: could not find function "flextable_to_rmd".

This error arises when when knitting to html file. This code was taken from flextable book. pandoc version I have 2.14.0.3. is there any function/code am I missing here?