When playing the Viking Spinner, the Mission can be seen above the Spin button.

For example:

If the Mission states Win 12.5M Coins it means that the player must earn 12.5M Coins while spinning the Vikings Spinner in order to receive their reward.

Viking Quest is divided into two different types of missions: Regular and Bonus.

Regular missions simply require the player to earn a certain amount of Coins in order to receive a reward.

The Bonus Wheel mission 

will test the player's ability to earn the stated number of coins needed by hitting three Bonus Wheel icons in a row.

With any other combination the progress bar will not move, but instead count Coins to your balance to help you continue playing!

All Coins won in the Viking Spinner are Raid Protected for three minutes after each press of the Viking Spin button.