How can I create a faceted ggplot histogram with multiple grouping variables in R?

I have a dataset with columns: product, category, sales. I want to create a histogram of sales faceted by both product and category.

Here’s a sample of my data:

library(dplyr)
library(ggplot2)

data <- data.frame(
  product = rep(c("A", "B", "C"), each = 10),
  category = rep(c("X", "Y"), 15),
  sales = sample(100:200, 30, replace = TRUE)
)

Tried: facet_grid(product ~ category).
Expected: Separate histograms for each product-category combo.
Result: Incorrect facetting, histograms overlapped.