If your Mac cannot meet the system requirements to use the CD/download, then you need to seek a refund for that software. You cannot use the license code to pay for online TurboTax. The pricing for online is very different. You have to pay the fee to use online.
To request a refund from TT ; https://support.turbotax.intuit.com/forms/refund-request.jsp
https://turbotax.intuit.com/personal-taxes/online/
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