For those transferring their farms from Apple to Android, I found these instructions, written by a supercell mod..
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The only way to transfer your farm from an iOS device to an Android device (or vice versa) is by using a Facebook account. You need to have access to both your iOS device and Android device to do this.
To transfer your farm, your iOS account needs to be connected to the correct Facebook account. For Android, open Hay Day and connect your farm to Facebook in the in-game settings by clicking the Facebook connection button.
Proceed as follows:
Open the Facebook app on the device where you have the farm you want to transfer and make sure you are logged in with the Facebook app and in the device's settings
Start the game on the device that has the farm you want to transfer, tap Settings and make sure your farm is connected to your Facebook account
Open the Facebook app on the device you want to transfer the farm to and make sure you are logged in here with the same Facebook account linked to your farm on the other device
Open the device's settings and make sure you are also logged in here with your Facebook account
Open the game on the new device and play the tutorial till you can tap the in-game Settings button.
Now tap "Connect to Facebook" and select the Facebook account you have the original farm attached to
If you are using an iOS device with iOS6 or higher, you will need to be logged in with Facebook in your device's settings. Open the device's settings and scroll down till you notice Facebook. Tap on it to check if you are logged in with your account. Always check if Hay Day is to be found in the list of applications that have access to your account and that this is turned on.
iPad RD | London, UK | GC: sapphireoceans | Level 75 | If YOU won't fill your own sugar/dairy boat, I certainly won't ~ also, manners are free