Sending Telegram Bot Conversions to Meta? Don't Reach for business_messaging

A bot was firing Subscribe and Purchase events from Telegram straight to Meta's Conversions API, and every call came back with a 400: "error_user_title" : "Missing Messaging Channel Parameter" , "error_user_msg" : "A messaging channel parameter is required when provided action source is business_messaging. Valid value could be messenger, whatsapp and instagram." The payload looked fine — event_name , event_time , a hashed external_id , and action_source: 'business_messaging' . So why the 400? The gotcha business_messaging is not a generic "it happened in a chat" source. Meta ties it to its own messaging products, and it demands a companion messaging_channel whose only valid values are messenger , whatsapp , instagram . Telegram isn't on that list — there's no channel you can hand it — so the request can never validate. The instinct is to try app next. Don't. app drags in a required app_data block: the extinfo array, advertiser tracking flags, the whole mobile-SDK surface. You don't have that from a bot, and you don't want to fake it. The fix For a self-hosted Telegram bot, the right source is plain other : " action_source " : " other " other has no extra mandatory fields. You need event_name , event_time , action_source , and a user_data with at least one identifier. A SHA-256 hashed Telegram user id as external_id is enough to clear the 400. One-line change. Making it actually attribute Not crashing is the low bar. To tie a Subscribe or Purchase back to the ad that caused it, you need the click id: Capture fbc . Your ad sends people to a deep link — t.me/yourbot?start=... . Meta appends fbclid to that destination. Pack the fbclid into the start payload, read it on /start , and build fbc = fb.1.[unix_time].[fbclid] . Send it in user_data next to external_id . This is the single biggest lever for matching. Purchase needs money. Add custom_data with value and currency , or there's no ROAS to compute later. Verify before you trust it. Events Manager has a Test Events tab — send with a test_event_code and watch the events land and match before you point real traffic at it. Dedupe if a web pixel fires the same events: same event_id on both sides and Meta collapses them. The 400 is a five-second fix. The attribution is the part that actually pays for itself.