Hello there, Bbs_pauljames.
Aside from the accounting method, you'll have to change the GST method to cash as well. I'll guide you how:
- Click GST.
- Click Edit GST, then choose Edit settings.
- Under GST method, choose Cash, then click Save.
- You'll receive a message, "Are you sure you want to make this change?", choose Yes.
I've attached a screenshot as your reference.

If you have more questions, just leave a comment below.