One way to upgrade your Divine Weapon is by summoning souls to activate or enhance your Divine Skills. Here are the guide to finish Learning Divine Skills quest.
1) Select a Divine Skill first
2) Then Summon souls, there are 5 Free Summons daily.
3) Click Fuse All the souls
How to get Coupons?
1) Click "Mall" in-game
2) Spend Crystal to Purchase Coupon
3) Right click the Coupon in the bag, and then you get the coupon points in coupon mall.