This is no longer a part of the World of Warcraft API. Instead use InviteUnit It was removed in patch 2.0.

Invite a player to your party.

InviteByName(playerName);

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Arguments

(String playerName)

playerName 

The name of the player you would like to invite to a group.

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Returns

nil

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Example

InviteByName("Dyselon");

Result

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Description

Invites the specified playerName to your group.