Clarification needed on private OAuth setup/AddOns (external add on)

I’m building an external integration. We’ve been issued an App ID and App Secret when creating a draft for an add-on, but I’m unsure what the next required setup steps are to get OAuth working privately (we don’t need this listed in the Add-on Store yet, just need to test OAuth integration.

I’m wondering - can we use OAuth privately with just an App ID/Secret, or do we need an Add-on Store submission/listing first?