Why is nick a little disappointed with Gatsby?

Gatsby is nervous because he wants Nick to agree to his plan of inviting Daisy over for tea. Nick tells Gatsby that he will help him. Gatsby offer him the chance to make money by joining him in some business he does on the side— that does not involve Meyer Wolfsheim. Nick is slightly offended that Gatsby wants to pay him for arranging the meeting with Daisy and refuses Gatsby’s offer, but still helps with the plan.