You need a new subscription for EXM 3.4, the old one is not good.
You can find on EXM 3.4 documentation :
Please be aware than when upgrading to EXM 3.4, a new subscription to the Sitecore Email Cloud is required.
This especially applies to existing subscribers of the Sitecore App Center product; Email Delivery. Email Delivery subscriptions will no longer be active in EXM 3.4 and you are no longer able to self-serve your subscription through the Sitecore App Center UI.
To ensure continuous service and for more information on how to migrate, how to subscribe and subscription pricing, please contact your local Sitecore representative immediately.