I was born to a US Citizen and since my mom never got me the US passport when I was a kid, I was a first time passport applicant over the age of 18, which is the Adult transmission route. https://nl.usembassy.gov/u-s-citizen-services/child-family-matters/claiming-citizenship-born-outside-united-states/ (I fall under the over age of 18 category on this website)
The documentation the consulate required was proof that my mom was a US Citizen and lived there for 5 years after the age of 14, so she brought her drivers license, medical papers, vaccination records, etc, and the immigration officer said I was “Born a US Citizen” so they issued me a passport.