User assign task to another user then reward, need Advice on what approach

Hi masters,

I wanted to create a sort of mobile game, but a function that I need keeps on bugging me and dont know where to start?

The game has multiple users, and i wanted to check what kind of approach i need to do if user A will assign a mission/quest with a corresponding reward to user B once completed, then once done user B will declare quest complete and user A will accept to give reward.

Should i use the network multiplayer service of unity? or any cloud database will do? any...

User assign task to another user then reward, need Advice on what approach