Annoyed with PATC Transmissions.
I send lots of PayPal invoices, and I wish I didn't have to; everything about their website sucks -- it fights the user every step of the way. PayPal keeps on helpfully "fixing" stuff that wasn't broken and breaking stuff that was working just fine in their ongoing effort to provide optimal user experience (or effing whatever). I wish a better payment service would gain some traction!
What this has to do with your post: it's possible they haven't yet sent you an invoice. But if my own experience is a guide, it's also possible they hit "Send" and PayPal helpfully decided they didn't mean to -- I have had the PayPal site go through all the motions including "Your invoice has been sent", without sending an invoice at all. Their tech support is just as useless as their site.