Business Central - unable to post purchase invoice with negative quantity (purchase return)

Hi, we noticed a vendor invoice for Jan 2021 was posted with different items and we over paid. (this invoice has been paid).  So I tried to create a new PO with negative quantity (I added the original items with negative quantity and added the actual items/amount) that showed a negative total equivalent to the over payment that we will be receiving from the vendor.  But sBC doesn't allow and show an error.    Are we missing something? Or is there a different way of processing this in BC.   Appreciate your thoughts on this. 

Description Context
Amount must be negative in Gen. Journal Line Journal Template Name='',Journal Batch Name='',Line No.='0'. Purchase Header: Invoice,xxxx61

I tried to create purchase credit memo directly from the posted purchase invoice (that has already been paid) 

Invoice xxxx26 is closed. The corrective credit memo will not be applied to the invoice.
Show applied entries | Skip | Create credit memo anyway
I am not sure if we can try "Create credit memo anyway".  Appreciate your thoughts on this.