How do I post a payment on account on a suppliers account? Its not a proforma, or a credit note?

Hi @accounts@novalux 

If you're expecting to receive an invoice at a later date, enter this as a Bill Payment in QBO.

(when logged in, go to https://app.qbo.intuit.com/app/billpayment)

You don't need to mark the Payment against a Bill.  Instead, this will record a credit on the supplier's register that you can subsequently use to clear the Bill in QBO.

Alternatively, you can enter as a Cheque (or Expense if paid on Credit Card).

Enter against the Supplier's Name.  Category = Accounts Payable.  VAT = NoVAT

This will create the same credit on the Supplier's register that you can subsequently use to clear the Bill in QBO.

Hope this helps.