Optional, and left empty on purpose. Paste a logged-in YouTube session as either a Cookie header string ('SAPISID=...; __Secure-3PSID=...; LOGIN_INFO=...') or a JSON object {name: value}. When supplied, the actor opens /about as the logged-in user, clicks 'View email address', and intercepts the revealed email. Every cookie you paste is bound to .youtube.com, Layer 3 only runs for channels the first two layers could not solve, and it is held to three concurrent browsers no matter what concurrency says. Leave empty to skip Layer 3: the run still works, and channels that keep their address behind the reveal button simply come back as not_found. YouTube can still answer with a captcha even with a valid session, in which case that channel falls through to not_found as well.
Example:SAPISID=PASTE_YOUR_OWN_SESSION_HERE; __Secure-3PSID=PASTE_YOUR_OWN_SESSION_HERE; LOGIN_INFO=PASTE_YOUR_OWN_SESSION_HERE