What the message should contain
Show the actual items with their images and chosen variants, the total as it stood with delivery stated, and one obvious route back that restores the cart exactly. Address the statistically ordinary obstacles in plain lines: the delivery window, the returns promise, a contact route for questions. If a specific obstacle is known for that product - a sizing doubt that support sees constantly - the message for that cart can answer it directly. Keep the tone that of a shopkeeper who noticed you left your list on the counter: helpful, brief, and entirely without pressure theatre or countdown devices.