Your first customers rarely come from a funnel. They come from people who already trust how you talk.
Talk in public like you talk when you are trying to help.
Before you hire: ask who writes the first draft.
If the answer is a junior then polish, you are buying polish. If it is the person on the call, you are buying taste.
How:
If your brand voice doc says "friendly but professional, bold but not aggressive, casual but premium," you do not have a voice.
You have a mood board with anxiety.