If you had an old WU API key, that stopped working last year. You have to have a new WU/TWC API key to use with the current api.weather.com API.
How to get a WU/TWC API Key
Use your browser to open
https://www.wunderground.com/member/api-keys If you are not logged in, you will be asked to. The system will also verify that you have a PWS uploading to the system.
You will then see a blank box below “Your API keys”.
Agree to the new Terms and Conditions by clicking in the small box next to “I agree”, click on the blue “GENERATE” box, and your new key will be created.
The key will be masked on the screen, but you can use the “Show” link below the box to see it.
There is also another blue box, which, when clicked, copies the key to your clipboard.