If you send through an email service such as Klaviyo or Omnisend, pass these variables to that service as a Shopify Flow event and you can include live values in the email body.
Discount Deck writes coupon information to a customer metafield, and the account page reads it from there.The Shopify Flow trigger fires at the moment Discount Deck writes that metafield, which is the moment the customer can see the coupon on their account page.