Hi - I upgraded to Scrivener 3 for $25. I downloaded the application, but the .dmg will not mount when I click or double-click on it, so I cannot install. I have a serial number for 3. I am running High Sierra 10.13.1 on a mid-2012 MacBook Air. I do not have Scrivener 2 open. I re-downloaded a fresh copy of the 3 .dmg and it still doesn't mount. If I cannot install this, will have to ask for a refund to my PayPal account. Thanks for any help/info you can provide ASAP.