Mapping alpha to continuous variable in geom_tile()/geom_raster()

I am trying to convert a heatmap I created with ggplot to a plotly object. Everything works fine, except no matter what I do, it won't translate the alpha values (I have tried both having it as aes- what I want- but also giving it a random value and it won't work. This is the ggplot code and output, which works fine:

I have tried both geom tile and geom raster and none of them seem to work.

 plot <- datos%>%
    ggplot(aes(Var2, Var1, fill = value,  alpha = dum,
text = paste("<b>Edad:</b>", Var2, "<br>",
                                                    "<b>Año:</b>", Var1, "<br>",
                                                    "<b> Año de nacimiento: </b>", (Var1 - Var2), "<br>",
                                                    "<b>Renta relativa:</b>", format(value, 
                                                                              big.mark = ".", 
                                                                              scientific = FALSE, 
                                                                              digits = 2))))+
  geom_raster()+
  scale_alpha(range = c(0.6, 1))+
  scale_x_continuous(breaks = seq(20, 75, by = 5), limits = c(20, 80))+
  scale_y_continuous(breaks = seq(2008, 2016, by = 2 ), limits = c(2008, 2016))+
  theme_minimal()

ggplot output (with a little more formatting:

ggplotly output (just doing ggplotly(plot)):

Comienza reproduciendo el ejemplo proporcionado con ggplotly(plot), comparando geom_raster() y geom_tile(), así como valores de alpha mapeados y fijos. Sigue la ruta de conversión de ggplotly para la estética alpha y verifica el resultado frente a la salida original de ggplot. Se considera terminado cuando los valores continuos de alpha se conservan en el mapa de calor interactivo convertido.