How do I use an International address for a South African company?

Hello there, @greg-marfire-co. Welcome to QuickBooks Community!

Just to clarify, are you referring to add an international address from the settings? If so, adding an international address for a company that is subscribed to another specific version of QuickBooks Online is unavailable. You have to use a specific QBO country version to where your company is located. Since you're currently using a South African company, you're required to enter a place located in that region.
 

If you'll want to correct the version of your QuickBooks, you have an option to cancel your subscription to prevent future charges. You can click this article for the complete steps: Cancel your QuickBooks Online subscription. 

Once done, you can utilize this link and scroll down to select the correct region for you. Then, sign up. This way, you'll be able to use the address you want for your QuickBooks Online account.

Please let me know if you have other questions as you go along with QuickBooks. I'm right here to assist you anytime. Stay safe and be well, greg-marfire-co.

@greg-marfire-co 

Where is the company located? Is it your sister company or another branch?