There are not many ways to earn coupons, only 3 ways

1. Recharge this, everyone knows it. 2. Go to the exchange to sell things. 3. Sometimes it is possible to get them during activities. A little but almost impossible

If you are a non-RMB player, just sell materials or cards. You can also sell other things, but this method is difficult to earn some rolls

You'd better Just top up your money