OWM Weather uses 3 OpenWeatherMap APIs to collect the data:
Weather 2.5 (current weather)
Forecast 2.5 (5 day / 3 hour forecast)
One Call 2.5 (Hourly forecast for 48 hours / Daily forecast for 8 days)
The recently updated OpenWeatherMap pricing list shows that Weather 2.5 and Forecast 2.5 are still part of the free plan. The latest One Call 3.0 is now “pay as you call”. I spoke to OpenWeatherMap support a while back and they ensured me that version 2.5 will stay free forever. This doesn’t seem to be the case since your API key is rejected. When I take your url from the error message and swap the key with mine, it works. That means older keys have different permissions than newly created keys.
I am going to contact OpenWeatherMap support to get to the bottom of it.