ttMETA mboxName as undefined

Hi Experts,

I have implemented ttMETA plugin using Adobe Launch. The code I have picked from target help doc.

However I am seeing undefined under "MboxName":

CODE OF ttMETA:
window.ttMETA.push(
{
'CampaignName': token["activity.name"],
'CampaignId' : token["activity.id"],
'RecipeName': token["experience.name"],
'RecipeId': token["experience.id"],
'OfferId': token["option.id"],
'OfferName': token["option.name"],
'MboxName': e.detail.mbox
});

RESPONSE of ttMETA:

CampaignId: "318808"

CampaignName: "POC"

MboxName: undefined

OfferId: "3"

OfferName: "Offer3"

RecipeId: "1"

RecipeName: "Experience B"


Can anybody advise why am I getting this undefined under mbox name ?