Unknown apps greyed out after update to Oreo?

[miles4000]

After recently upgrading my Sprint Samsung S7 to Oreo 8.0, I lost the Amazon Appstore app. I noticed this when trying to start an app I got from the store years ago (mSecure). So when I went to re-install Amazon Appstore, it won't let me do it because "Install Unknown App" list apps are all grey out? I called Samsung but they were no help. They mentioned maybe my Corp Email is locking this out now? Any ideas on how I can get around this issue?

 

[Rukbat]

Go into Settings and look for unknown. Then look for "install unknown apps". Then select whichever app you're using to install the Amazon App Store app (your browser?)

 

[miles4000]

That is the problem, the browser and all other apps listed are grey out to enable it.