If you just signed up then it can take a couple hours until the key works again. You could have kept your old key and just subscribed to the API too. It’s been 9 hours, still not working?
Although i struggled with this for a while, i ended up using the Norwegian Meteorological Institute integration (it’s an addon) simpler to use and configured
I also had a problem with the Openweathermap.org API in version 3.0, when I had to insert the API into HA, during integration. I got Invalid API, and couldn’t proceed. What did the trick for me was that there should ONLY be ONE Active API on your Openweather account. You can find it under your profile. This worked for me!
I was able to solve the problem by deleting the default API key in OpenWeatherMap. I then no longer got the invalid error in HomeAssistant and was able to complete the integration. Maybe this will help everyone finally.