Hi thereI’ve got a trial for the simple plan. Where do I add my payment details on the invoice. And can customers just click on a link to pay with a card or PayPal?

Welcome to the Community, @info747.

You can modify the default message for invoices to include your bank details in QuickBooks Online. However, it's not recommended to add this type of information for the safety of your banking information.

In case you want to push through the process, here are the steps:

1. Click the Gear icon in the upper-right corner and select Custom Form Styles. 
2. Search for the invoice template. 
3. Press the Edit option below the Action column. 
4. Go to the Content tab.
5. Choose the pencil icon in the bottom-right corner. 
6. Add the bank details under the Message to customer field.
7. Tick Done. 

For your second question, yes, you can let your customers pay by clicking the Pay now button from the invoice you're sending to them.

I recommend you visit the Create an invoice your customer can pay online article for future reference. It contains information about how you can accept payments online.

I want to make sure this is taken care of for you. If you have any other concerns, post a comment below. I’ll pop right back in to assist further. Have a good one.

@info747 

As additional option, you may also utilize this payment service. It supports QBO to send and receive payment in Australia.

https://veem.grsm.io/veems

Hope it helps.