Category doesn’t show on Mailerlite

Hi,
I am trying to separate my customers by the kind of items they buy but when I try to create a welcome email after the customers bought from a hidden category the category doesn’t show on Mailerlite like the ones that are not hidden.

This is something crucial so that only people that buy from the different categories receive emails related to that kind of product.

I’ve contacted them and it seems that they can’t resolve the problem. Could the developer do something about this issue?

Many thanks,
Denise