NOT AVAILABLE: Bumble retired the API these routes speak. Its endpoint answers every call, the anonymous handshake included, with 'Session not found (0030-3001-0051)', and the Bumble app does not use that endpoint at all: it speaks a binary protocol over a TLS socket to bma.bumble.com:443. No credentials get through until that transport is built, so these calls answer 502 instead of pretending to sign in. Read the signed-in Bumble account's inbox, or one conversation in full when conversation_id is given.