The following chapter of our guide to Assassin's Creed Odyssey describes the Debt Collector mission.
After talking to Marocs, you will learn that Phoebe was kidnapped. She is kept on the Ktymena Beach. When you reach the place, the protagonist will hide in the grass and start quietly eliminating enemies. Use this opportunity to train stealth attacks - these are very efficient, as they will instantly kill (or at least heavily damage) the enemy, hence allowing you to save time. Once you rid the area of enemies, free the girl.
Now go to Sami - a city near the Koliadai tower. There, you will find Duris the merchant, from whom you need collect the debt. You have three ways of solving this - either destroy his vases to force him to pay up, allow him not to pay (he will give you a sword as a token of gratitude) or kill him.
Go to Marcos and inform him of what you've done. Then, follow Drucilla to her workshop, where you should unlock the ability to use the bow. Test the new weapon by shooting targets - the mission will end successfully. Reward: +825 XP.