Level 1

I have applied a credit memo but the invoice still shows "open"

I have had a problem with credit memos recently.  I created an invoice in QB (2015 for Mac).  Customer paid with PayPal.  I haven't found a better way to credit a QB invoice when a customer pays this way, so I created a credit memo for the amount of the invoice and applied the existing credit to it.  However, the invoice is still showing as "open."  This has actually happened twice. 

In one instance I thought I would start over, so I deleted the credit memo and created a new one.  Now, the "open balance" for that customer has doubled and I have no idea what's going on!

Can someone please help!?