I used to test flow sensors by blowing air through them.
And that minimum flow is due to friction/leakage.
Get it working before hooking it up to the Pi.
Use 5V and a led/resistor to 5 V, puff some air through it and see if the led goes on/off.
It has a hall effect sensor so learn how those work.
8 hours wasted?
Well if you buy stuff from Amazon without a clue how they work, you will be in for some learning.
That's why I buy from Adafruit, Sparkfun etc you get real datasheets and most times even code and tutorials.
8 hours and what price do you put on those hours?
Sure it may have been cheaper to buy, but it has not been cheaper to use.
Then there is the time we have put in helping you
For better accuracy a small micro controller can figure out the flow rate and be read via i2c at the PI's convenience.
I use 8 pin micros for this sort of stuff.
What 8 pin micros do you use?
PSoC 1 - CY8C24123A, it uses i2c for programming but then I can use the same pins for comms.
This leaves 4 pins for stuff, digital, PWM, ADC, DAC etc
I'm dancing on Rainbows.
Raspberries are not Apples or Oranges