From Second Life Wiki

Message Layout

{
	InviteGroupRequest Low NotTrusted Unencoded
	{
		AgentData	Single
		{	AgentID		LLUUID	}	
		{	SessionID	LLUUID	}
	}
	{
		GroupData	Single
		{	GroupID		LLUUID	}
	}
	{
		InviteData	Variable
		{	InviteeID	LLUUID	}
		{	RoleID		LLUUID	}
	}
}

Usage and Notes

Used to invite any number of agents into the group (so long as they all fit in the packet). The requesting agent must have invite powers within the group to be able to invite other agents into the group.

InviteeID - The agent ID of the agent you want to invite into the group.

RoleID - The role ID of the role you want to invite the invitee into.