Seems like a lousy company to me.
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My conclusion, if you use them, just stick to the free plan, because that's all it's good for.
https://www.alphavantage.co/
YC backs questionable companies to the most fraudulent, but this is in the rates of less than 3% (1).
The best way for you to make this company better is to take your dollars else where.
(1) https://www.lesswrong.com/posts/ji4cvzir2qdpALLHo/ycombinato...