I’d say one reason Mikey didn’t hand the money over right away was to string along Roth because he knew if he paid him right away when they met then their plan is in motion to kill him. The longer he strings Roth along the more time he buys himself no matter what. Just him slow playing his hand while trying to figure out who turned on him.
Also he had to bring the money I think because Roth had people watching as he mentioned Mike bringing the money to the island. If it doesn’t turn up then he’ll think for sure there is no deal
Sure thing the real reason for courier! Fredo was to reveal the traitor in the family “who turned on him”
to Michael
We, the audience already knew [courtesy of Ola's late night phone call to Fredo]
it was you, Fredo -- you broke our hearts! -- you broke our hearts!
- Michael and Fredo having drinks in Havana
Michael: Later on in the evening we're all invited to the Presidential Palace reception, to bring in the New Year. After it's over - they're gonna take me home in a military car -- alone -- for my protection Before I reach my hotel, I'll be assassinated
Michael
already knew that Roth's “plan is in motion to kill him”
after the New Year's Eve party as above ie: No more time to buy
Point taken about Michael bringing the money over “to string along Roth” although by then it seemed neither Michael nor Roth, were fooling or fooled by the other
Michael was all set to be murdered after the party with or without the $2 million but of course if it fell into Roth's lap, Roth will take it Bonus! and added bonus Michael's own money paying for his own murder
