Most funnels do not leak at the headline. They leak at the moment you ask people to do work. Forms are where intent goes to die, usually for reasons that have nothing to do with the offer.

the usual suspects

Too many fields, unclear error states, a submit button that gives no feedback, a layout that breaks on a mid-range phone. Each one is small. Together they quietly remove a slice of every campaign you run.

Never make someone guess whether their tap did anything.

The fastest wins are almost always subtractive. Ask for less, confirm more, and treat the form as the most important screen in the journey, because for your revenue, it usually is.