Note: the following information only applies to v2.1 and later.
The P&F app uses the stock data provider AlphaVantage to obtain price data for use in the app. This service is used by many stock analysis applications. However, AlphaVantage has recently moved to a "pay to use" model for adjusted daily stock prices - they originally provided these for free. All other available data is still free.
If you see the above message and you don't need adjusted prices, just change to a 'Price Time Interval' of 'Daily' from the Parameters screen.
If you really want adjusted daily close prices, then please see this article in this blog.