Welcome to the Community, Tracy.

The option to do a bank transfer on the invoice requires a Merchant Service processor. Yet, this feature is unavailable in QuickBooks Online (QBO) South Africa. You can instead utilize the Apps menu in QuickBooks to find alternative payment processing services that integrate with QBO South Africa to activate the payment button. 

Here's how:

1. Sign in to your QBO account.
2. Click Apps from the left panel.
3. Go to the Find Apps tab.
4. Enter online payment in the search bar or click the Browse category button to filter the results.

Moreover, you can check this article for a guide to manage the payments in QuickBooks: 

• Record the advance payment received from the customer.
• Record invoice payments in QuickBooks Online

I'm always here if you have other queries about payments. Please share it below. Have a nice day ahead.