How do I take preorders for a product that is still in stock? (Essent Preorder Back in Stock app)

Change the campaign's Show preorder button rule. Open the campaign → Preorder products tab and pick one of three options:

• When product is out of stock: Add to cart while you have stock, Preorder at 0 or less. Switches back to Add to cart automatically when you restock.
• Always: Preorder replaces Add to cart whatever the stock. Good for made-to-order items or a launch.
• When product is in stock: Preorder while stock is above 0, Sold out at 0. Good for building hype or long shipping times.

The opposite problem: preorder showing on in-stock items

• Your campaign is set to Always. Switch to When product is out of stock.
• Only add the variants that should be preorderable. Every variant in the campaign follows its rule.
• If the page loads with a sold-out variant selected, the preorder message shows first. Make an in-stock variant the first option.

Full guide: How preorder campaigns work.