I actually solved this pretty easily after reading all the posts, but not exactly what was posted worked for me.

in the MMM-OpenWeatherMapForecast module director, edit the MMM-OpenWeatherMapForecast.js file.

under defaults, change

Endpoint:

From

“https://api.openweathermap.org/data/2.5/onecall”

To

“https://api.openweathermap.org/data/3.0/onecall”

then use an api key created after you subscribed, this last step may or may not be needed, but coincidentally or not, the last api key I made after making the above change was what worked.