Since the latest update of Amazon Video, it adds more limits on HDCP requirements for accessing HD videos. Accordingly, now, if you want to download HD(1080P) content with Kigo, your computer needs to support at least HDCP 1.0. At the same time, please do not turn off the computer screen, sleep or hibernate your PC during the downloading process.
Please go to this page to check if your computer meets the requirements. Click the "V" icon and choose a specified version, such as "1.0", then tap on "Get HDCP Status" to check whether your device supports HDCP-enabled content or not. If you get a result as "HDCP is available for 1.0" or higher versions, then you are able to download HD videos from Amazon Prime Video.
If your device meets the requirements but you still fail to download videos, please send the latest log files of Kigo to us for further analysis. You can find them by going to the program, clicking the Menu button (on the upper right corner) > Open log file. You will see a "logs" folder, please send us all the log files in this folder.
And please also send us the screenshot of this page that shows the testing results that HDCP is available for 1.0 or above.