This post makes me super nervous.  I have not had this particular issue with Melio of double payments, but I need that bill pay system, I use it constantly.  Quickbooks has no other option that is better so it will be very disappointing overall if they cannot address these issues.  The person prior to me with this one particular client did have trouble with Melio.  When I came on board it was filled with failed payments.  When I deleted it, it affected the P&L and those transactions in QB and I do recall having quite a time cleaning that up when I first came on board.  Sounds like they need to hire more people in customer service.