Great work! I see that you're using Yahoo Finance data. Yahoo deprecated its API so your data could stop flowing at any time. You can try free services like Alpha Vantage [0] or Google Finance formulas in Google Sheets exposed as an CSV / JSON. Another way is to hook up a freemium service like IEX [1] and ask your users to BYOK - bring your own key. I use IEX for my stock watching browser extension [2] and eat the costs for my users. It's not too bad.
[0] https://www.alphavantage.co/
[1] https://iexcloud.io/
[2] https://finance.shan.io/stock-inspector-discover-new-compani...