Gunner Asch writes:

Im sure you have gotten a soft drink that was flat, or watered down,
or just plain nasty. This is due to either being out of CO2, or out of
syrup, generally.

Or out of ice over the cold plate flash chiller. Warm soda is flat soda.

Carbonator pumps put out way more than 100 psi. That's the CO2 pressure in
a carbonator tank that the pump must overcome to inject tap water, which is
why you need a pump to start with (tap water being way less than 100 psi).

http://www.truetex.com/carbonation.htm