geom_signif() not adding significance label to ggplot()

Question

I am making this plot:

Coded by:

plot <- ggplot(data3, aes(x=cond, y=value, fill=variable)) +
                 geom_boxplot() +
  labs(y='Dispersal Distance (km)') +
  scale_x_discrete(name='Dispersal Effort',
                   labels=c('min'='Minimal', 'med'='Medium', 'max'='Maximum')) +
  scale_fill_discrete(name="Distance Type",
                      limits=c("Euc_Dist", "CW_Dist"),
                      labels=c("Euclidean", "Least Cost Path"))

I want to add significant annotations to each of the grouped data. I.e., between the dispersal effort scenarios. When I've tried adding the geom_signif() I get errors. I've been following this guide. This is the code:

library(ggsignif)

plot + geom_signif(stat='identity',
              data=data.frame(x=c(0.7,1.7,2.7), 
                              xend=c(1.3, 2.3, 3.3),
                              y=c(800,800,800), 
                              annotation=c("*", "*", "*")),
              aes(x=x,
                  xend=xend,
                  y=y, 
                  yend=y, 
                  annotation=annotation))
  

plot(plot)

These are the errors:

Error in `geom_signif()`:
! Problem while computing aesthetics.
ℹ Error occurred in the 2nd layer.
Caused by error in `FUN()`:
! object 'variable' not found
Run `rlang::last_error()` to see where the error occurred.

QUESTION: Why aren't they being added?

Sample of my data:

structure(list(cond = structure(c(1L, 1L, 1L, 1L, 1L, 1L), levels = c("min", 
"med", "max"), class = "factor"), variable = structure(c(1L, 
1L, 1L, 1L, 1L, 1L), levels = c("Euc_Dist", "CW_Dist"), class = "factor"), 
    value = c(5.25, 3.196, 46.389, 136.696, 131.181, 65.873), 
    group = c("min Euc_Dist", "min Euc_Dist", "min Euc_Dist", 
    "min Euc_Dist", "min Euc_Dist", "min Euc_Dist")), row.names = c(NA,6L), class = "data.frame")