【Updated: 】
You can send coins once per day to each friend. You do not lose coins when you send Greeting Coins. You cannot change the number of coins that are sent. When receiving Greeting Coins, you can collect all Greeting Coins that were sent by a player across multiple days.
The period to accept Greeting Coins is six days. The duration expires on the seventh day and you will not be able to receive the expired Greeting Coins after that.