indoor lemon tree small 3 ft leafs sweat

Question

is the sap normal

Answer 1

This is likely transpiration.

https://www.gardeningknowhow.com/houseplants/hpgen/guttation-in-plants.htm

If the sap is sticky then you likely have an infestation and this is honeydew.
Treat the plant with Neem Oil.

https://www.gardeningknowhow.com/garden-how-to/info/what-is-honeydew.htm
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm