I'd like to mention a couple of things, as I've had a fair number of interactions with Melio.  Fortunately, the severity of my issues have paled next to some that I've read here.  Anyway, I've reached them through two different addresses, "[email address removed]" (identified as "QBO Bill Pay Support"), and "[email address removed]" (identified as "Melio Support").  The latter seems to be most often associated with automatic responses.

1. There have been times where they've taken a while to get back to me - however, when they have, they've always been extremely thorough in addressing my issues - even to the point of getting back to me after the fact to see if everything has been resolved.  It's been quality support - but I'm guessing they're extremely under-staffed, like maybe somebody under-estimated the scope of taking on QBO.  (personally, I can understand why few people might want that job!)

2. Try out the Meliopayments.com site.  You don't even need to sign up for it - just use the "log in with Intuit".  If you're logged into QBO, you'll get right in.  It'll be shocking to see how differently everything is set up - it's a sleeker interface, but different enough in some aspects that it can be hard to find everything.  But so far I've found any info that's available in Melio within QBO.  The Bills and Payments also coordinate with QBO just as they do within QBO.  I've been going back and forth - using one when I hit a roadblock with the other.  I still haven't determined which one I prefer, though I'm leaning toward the meliopayments.com site.