It appears the plan with pricing doesn't include the weather data, just the transformation. You still need keys to the ultimate source.
I do feel the pain though. I moved to WeatherKit REST API when they stopped Dark Sky. The tiny amount of calls I make were free and easy in Dark Sky. In WeatherKit it is still free, but I had to figure out how to have my server generate JWT tokens which is a grade 2 pain in the ass on the 0 to 10 scale. (Also, the APIs are still marked as "beta". If you are killing a service and replacing it with a new one, maybe nail down that new one before cut over day? They are also sadly vague, the kind of stuff a programmer jots in because comments are required. If there is 3mm of rain followed by 50mm of snow, what does the precipitationAmount field have? The documentation says "The amount of precipitation forecasted to occur during the day, in millimeters.". Thanks, 12 words to tell me nothing. )