Mandatory double drop down selection

[Alkazim-DBT]

WHAT

Scenario -

User has to create a Product Record which asks you to select a main category from a drop down and following this type in your sub-category in a free form below it (see attached)

WHY

We now have a definitive list of sub categories that relate to your main category selection. I wanted to propose the attached and wanted to know if anyone had created a similar component in another gov.uk service? Happy to get some feedback on the proposed design too!

Both fields are mandatory and a product record cannot be created with out both selected.

HOW