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)):

Start by reproducing the supplied example with ggplotly(plot), comparing geom_raster() and geom_tile() and both mapped and fixed alpha values. Trace the ggplotly conversion path for the alpha aesthetic and verify the result against the original ggplot output. Done means continuous alpha values are preserved in the converted interactive heatmap.