Does anybody know of a proven app for selling in all Amazon markets and integrating with QBO in Australia?

QuickBooks Online integrates with hundreds of third-party apps, Timbtp. Although, we're unable to recommend one. 

You can always visit our App store so you can check the list of third-party apps. Just click the Flag drop-down arrow, then select AU (refer to my screenshot below).

Once you're able to choose the perfect app that suits your needs, here's how you can link it to our program: 

1. Click Apps.
2. Enter the name in the Search for an app field.
3. Click Get app now.

Get in touch with us if you need further help. We're here to lend a hand. 

hi @timbtp ,

You may explore an inventory managment app to integrate your QBO and Amazon as marketplace.

http://www.primaseller.com/?utm_source=Affiliate&fp_ref=primaseller

https://go.tradegecko.com/register?code=fiat-lux

We know another solution has Australian office in Victoria. PM me your contact detail to let them call you directly.