Where do the Coins come from?

Coin sources
SourceRule
Play time 1 Coin per hour in the game, up to 4 a day; a Coin button fills while you play and you click it each hour
Daily tasks 1 Coin per task, 4 tasks, up to 4 a day
Add Coin 1 Coin for 1,000,000 Noah, once a day; counts toward the 8
Reset 09:00 server time every day

What are the four tasks?

  1. Defeat 30 monsters above your level.
  2. Complete the Find Spy quest.
  3. Complete Juraid Mountain or Border Defense War.
  4. Upgrade any item via the Anvil.

Why does the ninth Coin never come?

The announcement spells out both orders. 1 Add Coin + 4 tasks + 3 hours = 8, so the fourth hour pays nothing. 1 Add Coin + 3 tasks + 4 hours = 8, so the fourth task pays nothing. And if you already have 4 from play time and 4 from tasks, the Add Coin button won't sell you a ninth. Only buy the Noah Coin early if you know you won't hit 8 through play and tasks.

Does switching characters reset the tasks?

No. The event is account-based: once four tasks have paid out on one character, another character on the same account gets nothing from the same tasks that day. Do the Juraid Mountain or Border Defense War run on the character that will actually play it.

What do the Coins buy?

Exchange list in the event window
ItemPiecesCoins
Scroll of Life 1 1
Scroll of Protection 1 1
Scroll of Weapon Enchant 1 3
Scroll of Armor Enchant 1 3
Scroll of Ascent 1 5
Monster Stone 1 10
[Event Emblem] Voucher (3 Days) 1 20
Speed-Up Potion 3 30
Alencia Wing Exchange Coupon (15 Days) 1 100
Green Treasure Chest 1 150

At 8 Coins a day, the Alencia Wing coupon takes 13 full days and the Green Treasure Chest takes 19, so the chest needed nearly every day of the August 26 to September 21 run.

Source · steamcommunity.comNTTGame: Coin Event announcement on Steam

FAQ

Where is the Coin Event button?
Bottom-left corner of the screen after you log in. Clicking it opens the event window with your Coins, tasks and the exchange list.
Can I trade the items I buy with Coins?
It depends on the item. The event window shows the trade, sale and storage status of each reward, so check it there before you spend.
Is the Coin Event the same as Daily Coin Exchange?
No. Daily Coin Exchange is a separate Juraid Mountain event from the same patch: 2 Daily Coins for a win, 1 for a loss, and 30 of them buy a Solar Tattoo from [Fortune Teller] Mekin.