Is a Tax Code specific to the Country where the subsidiary is (based on the subsidiary record)? For example, I have a tax code linked to UK but in the Subsidiary field of the tax code I’ve linked it to an AU subsidiary as well. When I create a transaction in the AU subsidiary, I do not see the UK tax code although it is linked to the AU subsidiary.

Doesn't seem to make sense. What are you actually trying to do, in plain English?

An AU subsidiary pays and collects VAT on sales in the UK. We need track it in a separate tax code. So I edited the UK tax code used in our UK subsidiary to associated the AU subsidiary with it.

It is not an AU subsidiary if it is collecting GB VAT

It is an AU subsidiary. We are also paying AU taxes. I think this is the reason why we need to pay import VAT (UK) for sales to UK online: https://www.alliotts.com/articles/brexit-information-for-australian-businesses/

Then i'm wrong. Sorry!

The nexuses are Australia and United Kingdom.

So this doesn't apply

No worries and thanks.

There will probably be a suiteanswer for this

Aha! I spoke too soon. It’s a nexus issue. Thank you so much!

The issue is legacy tax engine more than anything really - the nexus structure does not consider multiple tax registrations and as such multiple nexuses per entity is just about useless in a real world scenario. You can create additional tax types for the same subsidary if you need a work around - thne you can define additional tax codes and control accounts for any/multiple scenarios but it is a pain to manage somewhat.