To transfer your city, the account on your Apple device must be connected to Game Center, and the game on your Android must be connected to Google+.
▼To transfer from iOS→Android:
Starting in iOS: Go (in-game) to _Settings_ → _Account_ → _Link Device_ → _This is the original device_ and write down the code you receive.
Now go to your Android device: Go (in-game) to _Settings_ → _Account_ → _Link Device_ → _This is the new device_ and input the code from earlier.
▼To transfer from Android → iOS:
Starting with your Android, go (in-game) to _Settings_ → _Account_ → _Link Device_ → _This is the original device_ and write down the code you receive.
Now go to your iOS device: Go (in-game) to _Settings_ → _Account_ → _Link Device_ → _This is the new device_ and input the code from earlier.
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Game Guide for Age Of Warring Empire