AP downpayment - downpayment with Invoice

Hello,

I am trying to implement the AP downpayment flow.

The gap from the standard SAP is that prior to posting a downpayment I receive an invoice, that has to be registrated in accounting:

1. Downpayment invoice

Downpayment account = Vendor

2. Downpayment (preferably posted by F110)

Vendor = Bank account

3. Invoice

Expence = Vendor

4. Payment (for delta: invoice - downpayment) - (preferably posted by F110)

Vendor = Bank account

5. Clearing

Vendor = Downpayment account

The question is:

how did you implement this in SAP? we thought about a special G/L indicator then its reversal for steps 1 and 5.

Thank you,

Oana