wrapper.swift

import Passbase

class MyPassbaseWrapper {

   static func initialisePassbase:(_ apiKey: String) {
        PassbaseSDK.initialize(publishableApiKey: apiKey)
   }
}

These are the errors I get without making any changes to your code:

::ERROR:: swiftWrapper.swift:14:40: Expected '(' in argument list of function declaration
Current code: @objc static func initialisePassbase:(_ apiKey: String)
Xcode suggested change(fix): @objc static func initialisePassbase():(_ apiKey: String)

::ERROR:: swiftWrapper.swift:14:40: Expected '->' after function parameter tuple
Current code: @objc static func initialisePassbase:(_ apiKey: String)
Xcode suggested change(fix): @objc static func initialisePassbase -> (_ apiKey: String)

::ERROR:: swiftWrapper.swift:14:42: Tuple element cannot have two labels
Current code: @objc static func initialisePassbase:(_ apiKey: String)
Xcode suggested change(fix): @objc static func initialisePassbase:(String)

::ERROR:: swiftWrapper.swift:15:51: Cannot find 'apiKey' in scope
Current code: PassbaseSDK.initialize(publishableApiKey: apiKey)
Xcode suggested change(fix): NONE