Ah, I thought that you had already done this: you would need to Register your AmpliTube Orange product's Serial Number onto your User Account.
But if you do that now it may be more difficult to get a refund from Sweetwater.What is the exact name of the installer that you tried. What is its Modified date"? And where did it come from? Looking at the Sweetwater web page, it looks like they only send you a Serial Number?
I do not think that getting a refund from Sweetwater and buying directly from IK Multimedia would be different.
Everybody who open an IK Multimedia Account receives Serial Numbers for those 4 free products, but they may not be able to be installed on your OSX 10.8.5 system.
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The best thing to is to
contact Support, via here. There is a link at the top of the Search FAQs page to the Technical Support form, for some one to one investigation and help. Response time is usually within 2 working days (US (East Coast) Business hours, generally), but in the current circumstances please allow some more time.
Explain that
(a) you have bought AmpliTube Orange from Sweetwater, based on the System Requirements listed here:
https://www.ikmultimedia.com/products/orangecs/index.php?p=specs(b) the installer (supplied by Sweetwater?) says that OSX 10.9 is required,
(c) you are on 10.8.5.
And ask how to proceed to download, install and authorise the AmpliTube 4 software and the Orange gear.