My app is in internal testing on iTunes Connect, but I cannot promote it to external testing. It tells me that the test information is incomplete.
I have tried all sorts of things, including reading this doc and this doc on Apple and re-entering all the information again. Playing with the language specifier.
This is maddening, because this exact information worked for a previous build.
I checked and unchecked "Sign-in required" and Saved and the warning icon finally went away.
I had to check sign-in required and enter some dummy information. after I saved I went back and unchecked it, saved again; all good.
In my case all information was filled but still showing error "Complete test information is required to submit for review/external tester". I checkd, unchecked the sign in required option and saved it. It saved succeessfully :)
