Jenni,
If you're not using a 3rd party software provider for synchronised invoicing, but purely working within the MYOB system to generate and send your invoices, you should be able to switch off "Allow Online Invoice Payments" and BPAY.
In your MYOB dashboard, find the SETTINGS icon (looks like a cog wheel). It is just to the left of your business name in the top right corner. Click it, then click on "$ Sales Settings". In the Sales Settings screen, go to "Payments" (third option after Layout and Templates). Scroll down to Invoice Payment Options > Online Payments. If you have completed the mandatory upgrade, you'll see at the bottom "You have online payments activated". Click the link below that to Edit Preferences and you'll be in another Settings screen. Click the Online Invoice Payments drop down arrow and you'll find a toggled switch to slide left to NOT ALLOW Online invoice payments. Also untick the Accept BPAY option box, then SAVE.
Sorry no screenshots.