Stacked Barchart with total amount of bars text

Problem: I have a stacked barchart. Above each of the stacked bars I want to have a total number (i.e. the sum of the two bars - here: total). I tried to take usage of add_text but it did not work out as expected. Any suggestions what to change?

Remark: I do not want to cast the data.table object. The target frame on which the visualizations shall be made is new_frame.

Many thanks

Brief description of the problem

library(data.table)
library(plotly)

Animals <- c("giraffes", "orangutans", "monkeys")
SF_Zoo <- c(20, 14, 23)
LA_Zoo <- c(12, 18, 29)
data <- data.table(Animals, SF_Zoo, LA_Zoo)

new_frame <- data.table::melt(data, id.vars='Animals')

new_frame[, total := sum(value), by = Animals]

plot_ly(new_frame, x = ~Animals,
        y = ~value,
        type = 'bar',
        name = ~variable,
        text = ~paste(variable, value, total),
        textposition = 'auto',
        # insidetextfont = list(size = 10, color = 'black'),
        hovertext = ~paste(
            "<b>Hover text works IN/OUT</b><br>"),
        hoverinfo = 'text',
        hoverlabel = list(align = "left"),
        showlegend = TRUE) %>%
    add_text(
        visible = "legendonly",
        x= ~Animals,
        y = ~total,
        # showlegend = TRUE,
        name = "Titel",
        cliponaxis = FALSE,
        textfont = list(size = 10)
    )%>%
    layout(yaxis = list(title = 'Count'), barmode = 'stack')

Comienza con el ejemplo reproducible de R usando data.table::melt, plot_ly y add_text; después, inspecciona cómo los trazos de barras apiladas posicionan las etiquetas del total. Se considera terminado cuando se muestre la suma encima de cada barra apilada en new_frame sin hacer casting del objeto data.table.