Each time you get a new quest, there is a chance to get extra reward. Complete levels without losing and you will get reward when you complete the quest. You can check your progress in the level start menu.  

If you lose at least once per quest, reward will be lost. 

When the reward is lost your level start menu will look like this.

Important: Each quest has its own winning streak progress bar. If you have several quests, losing a level will fail the winning streak only for the quest which you used to open level.

When you keep winning you get also Traveller's Trophies - power-ups are added on the board when level starts. 

You can check current status on the level start screen. If you fail a level, power-ups are reset and you need to win 3 levels in a row again to get the maximum amount.