They coexist fine, and the order you'd naturally use is the right one: benzoyl peroxide first on clean, dry skin, let it absorb for a few minutes, then the snail essence, then moisturizer and sunscreen.
On the "deactivates" worry — it's reasonable chemistry instinct, but misapplied here. Benzoyl peroxide is a strong oxidizer (https://www.ncbi.nlm.nih.gov/books/NBK537220/), and it genuinely can degrade certain oxidation-sensitive neighbors: classic tretinoin is the famous documented case (https://pubmed.ncbi.nlm.nih.gov/9990414/), and pure vitamin C is a plausible one. Snail secretion filtrate isn't in that category. It's a humectant-rich soothing ingredient — mostly glycoproteins, hyaluronic-acid-like molecules, and glycolic traces — whose job is hydration and comfort, not a fragile active that needs protecting. There's no documented incompatibility, and BP's oxidative attention is not meaningfully "used up" by a hydrating layer above it.
Worth calibrating while you're here: snail mucin's realistic lane is hydration and barrier comfort — it's well tolerated and pleasant, but evidence for dramatic repair or anti-aging claims is limited and mostly small studies, so let it be a nice essence rather than a miracle. That soothing lane happens to pair well with BP, which runs drying; a hydrating layer over it is exactly what most BP users need.
One practical note: if the essence ever stings going on over freshly-applied BP, you're catching skin that's already irritated — give the BP more drying time, or move it to PM. Sting is information, not a required toll.