How to assign item to sub-category?

I've created some Categories and Sub-Categories:

- CAT A
-- SUBCAT A1
- CAT B
-- SUBCAT B1

If I create a new Payment, I see the Category combobox, but I can select only "A" and "B" categories, I cannot see "A1" and "B1". How can I assign it to a sub-category?

Thanks for this interesting tool! Regards

(Using Akaunting on-premise version 3.0.17)

Would also like to see the ability to select sub-categories on Expense entries. (On Premise v3.1.6)