When you submit your quarterly update, you'll see two sections, Business income and Business expenses. For more information on the categories in each section, see our Making Tax Digital for Income Tax category list article.
The categories in the Assign Nominal Codes to Income tax Categories window relate to the areas in your Chart of Accounts.
These are:
You can also add the categories in the wizard. Otherwise follow the assign the categories section below
Go to Nominal codes then select Assign Income Tax categories.
Select the relevant category in the Income tax category dropdown against the nominal code Name.
In Sage 50 Accounts v34 and above, you can use the Search function to narrow down the list of categories on this window.

Follow our submit quarterly update window article.