Webasto use red and green dots or spots to denote operating voltage of their voltage-critical heater components
Red = 12v
Green = 24v
The glow pin for the heater generation Air Top 3500ST should correctly be squared rather than the more typical circular, you are correct.
The correct Webasto part number for an Air Top 3500 ST 24v glow pin is 9004215B or 9004215A ( these numbers = the exact same part) - SEE LINK BELOW
https://www.butlertechnik.com/item/Webasto/Air-Top-Glow-Pin-24v/67O
YES - we have this glow pin in stock currently