[2019] Unlocking Co-op???

Originally posted by vacalpotan: What do you need to unlock party/coop option? What level or what mission or...???

Hey Vacalpotan. To play co-op, you need to reach the Campaign act "The Prayers" which is in Act I. This will unlock missions and assassinations, as well as co-op. After you finished the prayers, just click the Party tab and you'll be able to play with others!