Let's investigate why you encounter an invalid VAT number message, 2french.
The valid VAT Number for South Africa (ZA) region is comprised of 10 digits and starts with the number 4. Let's make sure you enter the correct format and the valid one when entering it in the Company settings.
You can also check your QuickBooks Online version to see if you're using the correct region.
If you enter the correct format and you're using the ZA region, I'd suggest reaching out to our Customer Support Team. They'll investigate what's causing this issue.
Here's how to reach them:
Click Help on the top menu.
Choose Contact us.
Enter invalid VAT number in the What can we help you with? field.