I have checked out this link: WHY alphavantage api is returning data for only 6 random dates? and Issue with AlphaVantage API (Deleted before it could be answered).
The sample of API call I am making is: https://www.alphavantage.co/query?function=TIME_SERIES_DAILY&symbol=AAPL&apikey=DEMO&outputsize=full
I have copied it from debug output to ensure it is as accurate as possible, with only change being replacing my API key with DEMO. While the API returns full result when tested in browser and Postman, its not working from the code. I tried making the API call from debug console and I got the same result, 6 random values.