There could be a myriad of reasons as to why the app isn't working, like a network connection issue, the app no longer being available on your device, the app developers doing maintenance preventing its use, or could be as simple as just needing a power cycle. You may even need an update to one of your devices. I would suggest checking out this link that will show a list of compatible devices, just to be sure yours is still compatible: https://www.primevideo.com/help?nodeId=GXMWDGNCPX2JLPFH&pop-up=1
If this app is the only one you are experiencing issues with, even after checking your device for an update and have unplugged it for a dew minutes, I suggest reaching out to the Prime Video app developers themselves and seeing if they can be of assistance. (They are the ones who decide which products their app goes on)
