The RO filter is clogged due to a build-up of waste water scale deposits. You will need to buy a new RO filter and go through the Descaling process.
To minimize the effect of waste water scale deposits, it is important that you always empty out the remaining waste water in the tap tank before refilling. The water left in the tap tank contains highly concentrated contaminants filtered out of your tap water. The level of the contaminants in the left-over water can be up to 6 times higher than the water coming out of the kitchen faucet. If this water is not discarded, the unit will develop scaling much faster and will require more frequent descaling. If you are in an area with hard water, you may need to descale more frequently.