Yep, that’s definitely the issue. On the Amazon product page, the only indication of the regional limitation is the words “for NA only.” Because it’s also described there as “travel-friendly,” It didn’t occur to me to look into whether this was a limitation of the LTE modem instead of, say, the power plug.
Now looking at the product on the Gl.iNet store, I can see that they do sell a global version. I’ve contacted customer support to see what my exchange options are.
Thanks for your help.