How do I set up a ‘Pay to’ account so I can select it when I’m creating an Invoice Payable?

You can only add a payee from the ‘Payments’ section of the app. 

To do this, open your app and go to ‘Payments’ > 'Send money' > add your supplier’s bank account as a recipient. 

Then, go back to your Bill draft (if it’s already auto saved) and select the ‘Pay from’ account where you added a new recipient. 

In your ‘Pay to' list, you can view and select your supplier’s bank account.