Fetch a single group with its tracked participants. Participant status tells you where each member stands: INVITED (add requested, not yet confirmed), PENDING (join request awaiting approval — carries a joinRequestId), JOINED, LEFT/REMOVED, or FAILED.

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.