1.Build the LP - converts?- If yes, move to step 2. If not, keep changing the traffic sources, message, style, features, product till something makes it convert. When it works, move to step 2.
2. Build the website like you have built the product but you haven't - If it converts build the product. If it doesn't, try step 3
3. Build a demo, simple video, all the stuff to show how your product works though you are yet to build the product - still doesn't convert? - Chuck it or pivot. If it works, build the product.