Below you can see that testing for external testers are turned off:
same for internal testing:
but when I transfer app, one of the criterias are not me
I just solved the transfer issue, you just need to expire your build from tester by following the steps below. and then app will available for transfer..
open your app and click on testflight then click on the icon of your app as shown in below screenshot.
The click on expire build.
Now you can transfer your app :)
We found that in addition to the other answers here, logging out and logging back in to iTunesConnect allowed us to continue after it was saying TestFlight was still enabled.
Do the same step as @Imran Iqbal answer, if your app is Sign-in Required, uncheck Sign-in Required also, like:
then, you can transfer app.
Creating new app version did it for me! Thanks!
For me it was localised test descriptions. Make sure you check that drop down list on the right and clear out info for all languages.
Not sure if this is going to help,
Check Users and Roles > TestFlight Beta Testers
Do you have a tester who is testing the app that you want to transfer?