Here is money for your troubles now give me the poison
This is a complication because Romeo's dream is foreshadowing what will happen later in the story.
This is a complication because Friar Lawrence's message was never delivered to Romeo so he does not know Juliet is faking her death.
This is a complication because Romeo wants to die because he thinks Juliet is dead. Once he sees Juliet he will take the poison but she will wake up shortly after. This means the plan will have been for nothing.
They're all dead
This is a complication because Romeo is confronted by Paris. In the end Paris is killed and Romeo takes the poison. Juliet's "death" has caused the death of both of them.
This is a complication because Juliet wakes up to her dead husband and kills herself with his dagger.
This is a complication because the poorly thought out plan that was supposed to stop the arranged marriage and allow Romeo and Juliet to be together has killed all three kids.