I don't know if you tried it either, but the number/letters have to be all together, with no spaces.
But yes, when you ship Express and whatnot, its the label number; it doesn't say tracking.
Try that, otherwise, ask the seller and see what they come up with. Sometimes (for me, too) it took a day or so to show up on the website.
Just depends on the post office it was shipped from too.