Adding north arrow and scalebar to ggmap plot

Question

I am having issues getting a north arrow and scale bar on my plot.

I built the plot using ggmap and I am using the ggsn package to get a north arrow/scalebar but I am getting the following error:

"Coordinate system already present. Adding new coordinate system, which will replace the existing one. Error in ggsn::scalebar(x.min = -160, x.max = 135, y.min = 15, y.max = 70, : transform should be logical."

Here is my reproducible code for the plot and the error detailed above:

bbox <- c(left = -160, bottom = 15, right = 135, top = 70)

latitude = c(49.38639, 50.68870, 50.77530, 49.86880, 39.31181, 37.05229)          
longitude = c(-121.45063, -120.36646, 50, -97.40836, 76.71748, -119.19536)

site_df = as.data.frame(cbind(latitude,longitude))

site_map = ggmap(get_stamenmap(bbox, maptype = "terrain-background", zoom = 2))+
              geom_point(data = site_df, aes(x = longitude, y = latitude), 
               size = 1.5, color = "orange")+
              geom_point(data = site_df, aes(x = longitude, y = latitude), 
               pch= 21, size = 2, color = "black")+
              theme_bw() + 
              labs(x = "Longitude", y = "Latitude")

site_map +
  coord_equal() + # needed for ggsn
  guides(alpha=FALSE, size=FALSE) + 
   ggsn::north(x.min = -160, x.max = 135, 
               y.min = 15, y.max = 70, scale = 0.2) + 
  ggsn::scalebar(x.min = -160, x.max = 135, 
                 y.min = 15, y.max = 70, 
                 dist = 5, dd2km = TRUE, 
                 model = "WGS84", height = 0.5, 
                 st.dist = 0.5)

I have also tried

site_map + 
  geom_sf(data = site_df, aes(x = longitude, y = latitude)) +
  annotation_scale(location = "bl", width_hint = 0.125) +
  annotation_north_arrow(location = "bl", which_north = "true",
                         height = unit(1, "cm"), width = unit(1, "cm"),
                         pad_x = unit(0.3, "cm"), pad_y = unit(1.2, "cm"),
                         style = north_arrow_orienteering) +
  coord_sf(xlim = c(-160, 135), ylim = c(15, 70))

But I get the error message:

"Coordinate system already present. Adding new coordinate system, which will replace the existing one. Error: stat_sf requires the following missing aesthetics: geometry Run rlang::last_error() to see where the error occurred. In addition: Warning message: Ignoring unknown aesthetics: x, y "

In addition, I am looking to add a legend that says "Sites" for the orange dot and I have used

site_map + theme(legend.position=c(0.9, 0.1))

for this but it does not display.

I would be grateful for any ideas or resources on this. I have researched several methods but none seem to work for this plot. Thanks!