Here is a starting point:
Recommended Cinnamon extract
Extract = Liters * ppm /10
Ex: 250ml at 80ppm
.250 L * 80 /10 = 2ml
This will probably have to be adjusted because cinnamon extract is not a standardized product. How much you need will be deterimined by how you make the extract, and the quality of the cinnamon you use, but it should be close.