How do I get TestFlight Redeem or Activation Code ?

I only helped one time a developer testing a beta version. But it was very easy, in the e-mail was a blue button "view in testflight" just below the app icon. Tapping on the button, testflight directly opened and asked to load the related beta app.

Hi,

you should receive an invitation by e-mail from the developer.

But why do you post this here in the GarageBand forum?

Greets

Oliver