Output issue with product SKU:SEN0170 Anemometer Wind Speed Sensor

Hello, I need help with this product: Anemometer Wind Speed Kit (0~5V, 0.1m/s Resolution, 0~30m/s Range) - DFRobot

I followed the wiki step by step using a 19.5V source for the anemometer and Arduino UNO for measurements but I only get a constant output value of 5V and it is not affected by the wind speed.

I thought there might be something wrong with my Arduino so I'm testing it separately now with a multimeter and I get a constant output value of 18.5 V.

Then I switched to a 12V source and now I get a constant output value of 11V. It seems to me that the anemometer doesn't work and it just has a constant output value that is close to the input source value. Can you please help me find a solution?

This is for a college project so I need to fix it asap.