I am creating a subgroup analyses forest plot with forestplot in R.
Here is the code snippet:

tm_new <- forest_theme(
  base_size = 10,
  ci_pch = 15,
  ci_col = "#762a83",
  ci_fill = "black",
  ci_alpha = 0.8,
  ci_lty = 1,
  ci_lwd = 1.5,
  ci_Theight = 0.2, 
  refline_lwd = gpar(lwd = 1, lty = "dashed", col = "grey20"),
  vertline_lwd = 1,
  vertline_lty = "dashed",
  vertline_col = "grey20",
  summary_fill = "#4575b4",
  summary_col = "#4575b4",
  summary_cex = 2
)

labeltext <- as.matrix(os_all[, c("Subgroup3", "HR (95% CI)", "space")])

forestplot(
  labeltext,
  mean = os_all$est3,
  lower = os_all$low3,
  upper = os_all$hi3,
  is.summary = c(rep(FALSE, nrow(os_all)-1), TRUE),
  ci.vertices = TRUE,
  clip = c(0, 4),
  xlab = "Hazard Ratio (95% CI)",
  xticks = c(0.5, 1, 2, 3),
  txt_gp = fpTxtGp(label = gpar(fontfamily = "", cex = 1),
               ticks = gpar(cex = 1),
               xlab = gpar(cex = 1.2)),
  col = fpColors(box = "darkblue", lines = "darkblue", zero = "black"),
  lwd.ci = 2,
  boxsize = 0.2,
  ci.vertices.height = 0.2,
  colgap = unit(6, "mm"),
  theme = tm_new
)

How can I add a dashed reference line at HR 1?

I tried adding the refline argument but it did not work