Cupra mode - make sure to switch to it if you just started your car, the car will still keep displaying Cupra mode but will keep the exhaust flap closed unless you switch to a different mode and then come back.
S gearbox (should be automatically in it if you switched to Cupra mode).
Push the car a bit, let off the gas suddenly at 3500 rpm.
Keep playing with a little bit of gas and then release at around 3500. You can litterally just tap it a little bit around this rpm and it should rumble/pop.
Going under 3000 - no bangs at all.
Going over 4000 - usually less bangs or less noticeable due to engine noise.
I disconnected my fake sound generator so it may be easier to hear.