Looking at this thread, it looks to be a common problem, and seems that the weather service updated their key format, and FSD has limitations for entering the key based on the old format. I cannot tell from that thread or looking around the internet whether there is currently a fix or not.
Have you tried contacting JPizzle on that site? Based on posts in that thread, he seems willing to share his key via PM. Or maybe a member here has a working key that they would be willing to share with you. Personally, I don't use FSD as my main dashboard and don't have the weather working, so I would not be able to help you in that regard.Yah.. I know. I've been asking around for ages with no luck

Have you tried contacting JPizzle on that site? Based on posts in that thread, he seems willing to share his key via PM. Or maybe a member here has a working key that they would be willing to share with you. Personally, I don't use FSD as my main dashboard and don't have the weather working, so I would not be able to help you in that regard.