Not Found
You can set the 404 page in two ways, the function is identical and follows the same logic as that passed to the get or post methods.
# these are equivalent
app$not_found <- \(req, res){
res$status <- 404L
res$send(htmltools::h2("404"))
}
app$set_404(\(req, res){
res$status <- 404L
res$send(htmltools::h2("Not found"))
})