1. Express my blessing: First of all, I would like to express my blessing to the newlyweds, thank them for their invitation, and hope they can have a beautiful wedding and a happy future.

2. Explain the reason: explain the reason why you can't be present, such as work, study or other important arrangements. At the same time, express your apologies and hope they can understand.

3. Apologize: Express your apologies and hope they can understand.

4. Offer compensation: If you think it is necessary, you can offer some compensation, such as giving them a gift or giving them a red envelope.

The following is an example of a reply:

"Dear (friend's name), I wish you a happy wedding! It's a pity that I can't share your joy there, because I have (reasons). But I'm really sorry, I hope you can understand. To make up for my regret that I can't be there, I want to give you a gift or a red envelope. I hope you can have a beautiful wedding and a happy future. Bless you again, and God bless you! "