What Self Leveling underlayments are compatible with electric floor heat?
Any high quality self-leveling underlayment can be used. Please check with the SLU manufacturer to see if any primer is required. Primer should be applied to subfloor before placing the heating product down and before covering with the SLU.
Custom Building Products self-leveler is available at many big box stores. Contact them at https://www.custombuildingproducts.com/ for product recommendations and instructions.