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Why are my AskSellerQuestion notifications are not being sent?
The AskSellerQuestion will notify the user only for "active listings".
The cases where the notifications are reported not received are the listings which have already been sold. So, there wont be any "AskSellerQuestion" notifications sent for this scenario. If the seller wants notification for all the member messages he receives, he should subscribe to either MyMessagesM2MMessage or MyMessagesM2MMessageHeader Notifications.