Originally Posted by Astrophsx

Sorry but Amex doesn't know the details of one's Venmo account. It's not as if these two companies are sharing information about their consumers. All Amex is seeing is two transactions for Venmo on one account. I'm not sure why this would raise red flags.

Venmo might have thought this was just a fake account. If he is an authorized user he may have put the same physical address as his mother's. Or.. if he signed up using her internet connection they might have shared the same IP address.