J.R. S. answered 10/24/20
Ph.D. University Professor with 10+ years Tutoring Experience
Lye = NaOH, or KOH, etc.
Epsom salt = MgSO4
Both are soluble in water so you would have...
2NaOH(aq) + MgSO4(aq) ==> Na2SO4 + Mg(OH)2(s)
What you would observe is the formation or a white precipitate, Mg(OH)2.