Percentage format for y axis in mschart

Ok, this is kind of driving me insane. Hopefully I'm just stupid and someone can point me to the right answer quickly. I'm trying to format the y-axis to be a percent rather than a number. Here is a simple example ...

library(officer)
library(mschart)
data = data.frame(x = c(1, 1, 2, 2, 3, 3),
                  y = c(.05, .05, .06, .06, .07, .07),
                  group = c("A", "B", "A", "B", "A", "B"))

output <- data %>%
  ms_barchart(x = "x", y = "y", group = "group") %>%
  chart_settings(dir = "vertical") %>%
  chart_data_labels(show_val = TRUE, show_legend_key = FALSE, num_fmt = "0.00%") %>%
  chart_labels(title = "", xlab = "", ylab = "")  %>%
  chart_ax_y(display = TRUE, limit_min = 0, num_fmt = "0.00") %>%
  chart_ax_x(major_tick_mark = "none")

doc <- read_pptx()
doc <- add_slide(doc, layout = "Title and Content", master = "Office Theme")
doc <- ph_with(doc, output, location = ph_location_fullsize())
print(doc, paste0(file.path(path.expand('~'),'Desktop'),"/num_fmt.pptx"))

The above code will not produce an error, but the format is not as desired.

Using num_fmt = "0.00%" in the chart_ax_y function produces the error when attempting to print the pptx file: Error in sprintf(str_, id, cross_id) : invalid format '%" s'; use format %s for character objects

Using num_fmt = "0.00\%\%" (this is what the mschart documentation says to do) in the chart_ax_y function produces the following error when trying to create the output object: Error: '\%' is an unrecognized escape in character string starting ""0.00\%"

Please help!