You can find the answers to many questions here, it’s very likely someone before experienced the same problem as you do. Otherwise you can also submit an issue ticket and wait for our help.
It means that after downloading license you have 72 hours for activating your software with the downloaded key. If you won't make it within that time, you'll have to log-in to your User Area account and re-download the license key one more time, because key looses its validity after exactly 72 hours after download.
This also implies you can't store such a keyfile somewhere on your disk forever (e.g. on an event of system crash and re-installing).
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