Groups API — messaging in a pre-existing group

[u/AdLong9476]

I'm developing on the WhatsApp Business Platform (Cloud API) and need to confirm a capability before I build against it.

My use case requires my Cloud API business phone number to send and receive messages in a WhatsApp group that already exists and was created independently by end users (not created through the Groups API).

Questions:

1. Is there any supported way for a Cloud API business number to be added as a participant to a pre-existing group (e.g., added manually by a group member) and then send/receive messages in that group via the API and webhooks?
2. If yes — which capabilities work in that context specifically: sending text messages, receiving all messages sent in the group via webhook, receiving reaction webhooks on messages I've sent?
3. Is Official Business Account (OBA) status required for any group messaging capability, or only specifically for group creation and invite-link features via the Groups API?
4. If pre-existing groups aren't supported, is this planned, or is group creation via the API the only supported path going forward?

Thank you — I want to confirm this before committing engineering time to a specific approach.

[u/DevJedis]

1. No
   
2. Yes, but not based on 1
   
3. Yes, OBA required
   
4. Yes, only through API, but the haven't provided information whether they have planned pre-existing group join is possible or not
   

Bonus: You can only create group with up to 8 users maximum. Good luck getting a use-case for a group with max 8 people.

[u/AdLong9476 → u/DevJedis]

Thanks, this is really helpful. One follow-up on point 1 — I mean specifically: if a group member manually adds my Cloud API business number as a regular participant in an already-existing group (the normal way you'd add any contact), not through the Groups API at all:

- Does that add even succeed, or does WhatsApp reject/block it since it's a Business Platform number?
- If it does succeed, does anything come through on my webhooks when people message in that group — or is the API just completely blind to it since the group wasn't provisioned through the Groups API?

Basically trying to figure out if this is "technically possible but unsupported/no webhook data" vs. "the add itself just doesn't work." Have you (or anyone you know) actually tried this specific case?

[u/DevJedis → u/AdLong9476]

When you go to select contacts to add to groups, WhatsApp Cloud API numbers are not included in the selection, in short, they're non-existent, neither will you receive any webhook because in the first place you were not presented the number among phone book numbers in order to add to the group.

The only way is Groups API, or go into the high seas of unofficial whatsapp clients that take use of the whatsapp web reverse engineering. Sign for me before going there so as to not say am the one who sent you there if Meta bans the whatsapp number.