Remove what’s been installed, and reboot. Silverlight is dead or soon dead. On all platforms. Adobe Flash is dead or soon dead. On all platforms. There’s an Adobe removal tool available from Adobe. I haven’t researched how Silverlight is removed, but I’d expect a removal tool downloaded from Microsoft.
https://www.amazon.com/gp/help/customer/display.html?nodeId=201422810
https://www.microsoft.com/getsilverlight/get-started/install/default
macOS 10.13 High Sierra supports HTML5, which meets the requirements for viewing video from Amazon Prime. Without add-ins.
If you want to stream output from your Mac to another display, your cabling and your display must all support high-definition content protection (HDCP).
https://www.amazon.com/gp/help/customer/display.html/ref=hp_left_v4_sib?ie=UTF8&nodeId=201460880
https://www.amazon.com/gp/help/customer/display.html?nodeId=201460980
If all that fails and if HDCP is available throughout, then if you have add-in anti-malware or add-on anti-virus, remove it per vendor instructions, and reboot. Same removal and reboot for add-on cleaning apps, and for add-on firewall-and-network-monitoring apps, and disable all browser extensions present. If you have any ad-blocking apps installed or configured or enabled anywhere here, disable it as part of this testing.
If the above doesn’t get this working, then I’d check with the folks at Amazon.
