Add up to 8 participants (per request) to a group by phone number.

A 200 does not guarantee membership. WhatsApp confirms each member asynchronously — participants appear as INVITED until confirmed JOINED (check via GET /api/wp-crm/groups/:orgId/:chatId). Users whose privacy settings block being added can only join via the invite link — share it as the reliable fallback.

Security:

• The organisationId in the URL must match the organisation your JWT was issued for — requests for a different organisation fail with 401.
• Requires CRM_ADMIN, ACCOUNT_OWNER, or CRM_BOT role; other roles receive 403.
• Groups are only supported on WHATSAPP_OFFICIAL channels whose number is an Official Business Account (OBA); ineligible numbers receive 422.