How can I apply the same tax code for customers that are not the primary subsidiary? If we make a SO or invoice the default tax code applies. I can only apply a different tax code to the primary subsidiary

That seems to be a limitation of using Multi-Subsidiary Customer feature. See SuiteAnswers #70186 https://netsuite.custhelp.com/app/answers/detail/a_id/70186/kw/multi%20subsidiary%20customer%20tax I hope that answers your question

That helped a lot. Thank you!