I'm using Swift 2.3 on Xcode 7.3.1 and when in AppDelegate I'm trying to import
import UserNotifications
UserNotifications
SWIFT_VERSION = 2.3
You can't simply mix swift2.3
and swift3
in a single project within single target and this is also not a recommended approach.
The error which you are getting is due to UserNotifications
framework. This framework has been added in xcode8
so you can't use this framework in xcode7.3.1
.
Also if you are planning to use swift2.3 in Xcode 8 then you have to use Legacy Swift Version
if you made it yes then you will be able to run your project which is in swift2.3, but you will be not able to use syntax of swift3.