Soit ... soit vs. Ou bien ... ou bien

Question

Are these two options interchangeable ??I was marked wrong for using it in one of your questiona

Accepted Answer

Hi A. Bryce.
Although you could use 'ou bien' instead of 'soit ... soit' in some cases, in this lesson you are being tested on the use of the latter so you would be marked wrong.
Bonne Continuation !

Answer

EDIT: Update after official answer was posted.

So independent from the correct answer to the quiz question.

Could someone come up with examples when only one of the conjunctions is grammatically correct/idiomatic?

I figured that they are interchangeable except that the "bien" adds emphasis on the distinction or on a consequence ("or else").

My impression is that you would more likely use "soit" when starting a sentence e.g. "Soit je gagne soit j'apprends.". But I think the following are fine as well:
"Ou (bien) je gagne ou (bien) j'apprends."

As far as I can tell, you could also add "ou (bien)" as second part to "soit":
"Soit je gagne ou bien j'apprends."