I signed up for https://home.openweathermap.org/ and when i pasted the API key on GWS, it says the key is not valid. Please help.
Silly question but I have to ask, was your computer connected to the internet at the time you tried to activate it?
It may be that you tried to enter the API key before it was fully registered try it again.
Or it may be that the newer OpenWeatherAPI is not supported by GWS.
GWS is pretty old and deprecated. Are you using GWS 2.0 or GWS 2.0.1 if it is 2.0.1 try uninstalling it and use GWS the previous version GWS 2.0.0. I think that 2.0.1 introduced many bugs and provided no improvements other that it runs on a Mac.
Ron
Samsung Developer Relations