Embedded data from external .CSV file does not appear on custom email

Hi, I was trying to create a custom email for survey distribution, however, when I used piped text -> embedded data -> RecipientFirstName in the body of the email message, it does not appear on the recipient's email message, but when they click the survey link, and answering the survey the same embedded data, appears throughout the survey and seems to have no problem, when in fact, they are from the same .CSV file. Any tips or tricks on how should I treat this.