Welcome to the Community, cklbookk.
Are you referring to send your receipts into QuickBooks via email? If so, this feature is unavailable in QuickBooks Online (AU) yet.
For now, our developers are rolling updates to have this option available to all of our users.
In the meantime, you'll want to upload the receipts from your computer and attach them to the transactions before sending them to your customer. Please see attached screenshot:
I also encourage you to visit our QuickBooks Blog to get the latest news and updates on what our product team is working on.
Feel free to visit us again here if you have any other concerns.