The daily charge is £15 if you pay in advance or on the same day, or £17.50 by midnight of the third day after travel. If you don't pay by midnight on the third day after travel in the zone, you will receive a Penalty Charge Notice (PCN).
If your vehicle is involved in a contravention on the red route, you'll be sent a Penalty Charge Notice (PCN) for £160. You need to pay this within 28 days. If you pay this within 14 or 21 days (it will say on the PCN), the amount will be reduced to £80.
About late fees, I found this: https://tfl.gov.uk/modes/driving/congestion-charge/paying-th...
And a PCN: https://tfl.gov.uk/modes/driving/red-routes/penalty-charge-n...