100 Mark 1920 Banknote Serial Number Question

I have the below banknote and I'm not sure if I'm reading the entry correctly:  100 Mark (Reichsbanknote) - Germany (1871-1948) – Numista

I have the serial number in the top right and bottom left U15136407 and a large Q under the signatures. This combination does not seem to be covered by the comments section…?

Your banknote is P#69b; it’s underprint letter is Q; the serial number prefix is U. You must’ve either missed it or mixed up the Q and U when reading for your combination.