The 2% cashback applies to all users who are members of the MagentaONE scheme and make payments for mobile and fixed-line bills* or top-up through the COSMOTE app or the What's Up app.
A basic requirement to benefit from the 2% cashback is that the payment is completed via the "Pay with payzy app" option.
*Payments for electricity, water, etc. bills do not qualify for the 2% cashback.