Here are a couple of steps you can try to recover the transfer:

Allow a few hours for the email to arrive, and have your friend check their spam folders.
If he/she definitely hasn't received it, cancel the transfer from your account and start again.
Check that the email address has been entered correctly.
Transfer the tickets through your account on our website instead of the application.
Try using a different browser
Try sending them to an alternative email address, if possible.