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There could be a number of issues.
1. Make sure the flow control is set properly. It could also be clogged. I would check that first.
2. Make sure the filter kit is the proper kit and that the filters are installed the correct sequence.
3. The tank could be a unit that requires pressure. Usually not the issue, but possible.
My guess is that the problem has to do with the flow control. An RO system usually produces only 20 gallons per day of water. If you have a flow control, that would severely limit the water into the system.
That is a snifter valve. You need to pressurize the tank to your working pressure. There is a diaphragm in there to equalize the pressure. However, it is uncommon for a RO system. That is an expansion tank.
My guess is still on the flow controller. I would check to see if you are getting any water to the tank connection. If so, then pressurize the tank to your water pressure level (40 - 60 PSI).
I recommend getting the manufacturer involved. This seems very odd to have an expansion tank on an RO system.